Lucius came for me three nights later. Kreacher woke me, upset and hand-wringing.

'The Young Malfoy is here. He has ordered Kreacher to wake Master Regulus. Kreacher said Master Regulus was sleeping, but the Malfoy did not listen.'

I rolled quickly out of bed, reaching for my robes and pulling them on as I spoke. 'I will deal with him, Kreacher. You are to stay here. Inside my wardrobe. I need you to … guard my dress robes.' It was my feeblest lie to date, but I carried on. 'If I'm not back by morning, go to Master Sirius and tell him what has happened, and who I went with.'

'The Blood Traitor?' Kreacher wailed. 'Master Regulus will not make Kreacher do such a thing! Mistress would not allow it!'

I paused in my dressing and dropped to my knees so that I could look him in the eyes. 'Kreacher will do this for me, because it will mean danger for whoever you go to. You wouldn't want to put Mother or Father in danger would you?'

'Kreacher would never do such a thing!'

'But you wouldn't mind if it was Sirius.'

A crafty look came into his eyes at that, I knew how to phrase my appeal.

'Sirius would be able to help me, while keeping Mother and Father safe. And if anything bad happened to him, well, it would make Mother very happy.'

'Kreacher understands. Master Regulus is very subtle. Kreacher will wait in the wardrobe, and the dress robes will be well guarded.'

I caught the back of his tea towel as he opened the door. 'I want you to take something to eat, and to sleep while you are in there. Your presence will be enough to keep them safe. It is important to me you are well rested.'

He shook his head at me, but did as I ordered, popping away only to return a moment later with sandwiches and an old blanket. 'Master Regulus is to be taking care of himself, not of elves who know what they are doing.'

'You're quire right,' I agreed, buttoning up my boots. I grabbed my mask and hood, and my satchel of Potions, too, then rushed downstairs to where Lucius waited.

He saw the satchel in my hands as I ran down the stairs as quietly as I could. 'You have anticipated me!' he whispered.

'Is someone hurt?'

He paused oddly before stating that someone was. That should have warned me.

When we Apparated to Malfoy Manor, I felt a moment of panic. Severus could have been hurt again, or there could be a problem with Narcissa and the baby. I had been researching methods of dealing with the most common battle injuries, but I knew next to nothing about obstetrics. Rational thought intruded and assured me Lucius would have taken Narcissa to St Mungo's.

He walked ahead of me, pace brisk, and did not look back until we reached the door to the third-best drawing room. There he paused, and turned to me before opening the door.

'Your patient is inside. I did not wish to be involved in this, but I came home and found that my wife's sister had made it my problem. I am hoping that you can redeem things a little.'

He stepped out of the doorway then, pushing the door itself inwards, and revealing the backs of my cousin Bellatrix and young Barty Crouch. They were leaning over something, but moved out of the way as they heard us enter.

I saw what it was, then, and I stepped back out of the room. Lucius had anticipated me, and left the door open. He muttered something to Bella and Barty, then shut it, with us outside.

'That … that thing …' I stuttered.

He put a steady hand on my shoulder. 'I know.'

'He –' I was guessing at the gender – 'was wearing Ministry Robes.'

Lucius took a breath. 'The Dark Lord believes he has information that is essential. Unfortunately, I was not at hand when the mission was proposed. Bellatrix and Bartemius took the matter in hand, and you have seen the result. The man is dying, Regulus. I need you to keep him alive, at least until we have our answer.'

The face that I had seen had been a swollen mass of gore, with skin purple and black with bruising and parts of the jaw and nose down to raw, oozing, flesh. Blood had been bubbling through his lips, which could have spoken of broken teeth or nose, or of something far less survivable.

'I'll do what I can,' I said, 'but I can't promise you anything.'

Lucius nodded and opened the door again. Barty had his wand out and pointed at the victim.

'Put it away!' Lucius snapped. 'Do you think the Dark Lord will reward you if you deliver him a corpse with no information?'

Barty growled at him, but did as he was told.

Bellatrix looked at me and a slow leer crept across her face. 'You've brought my handsome little cousin, Lucius. He often follows you. Is there something we should know?'

I frowned, but Lucius ignored her. 'Regulus is here to return the prisoner to a fit state.'

I stepped past them, elbowing Barty out of the way rather viciously if truth be told. The man did not react to me as I knelt beside him, though whether that was because it was beyond him physically or mentally, I could not tell. Barty leaned over me as I felt for a pulse, my hand slipping on the blood that covered the man's neck.

'Can you get them out of here?' I asked Lucius.

With a curt nod, he gathered up the other two and took them from the room.

'Can you hear me?' I asked.

There was no response.

I turned to my satchel and began to mix a restorative. I added an ample splash of blood replenishers, but without a close investigation, it would be hard to know what else would help rather than harm.

I summoned one of the Malfoy house-elves and sent him for water, cloths and alcohol. Together we cleaned up the man as much as was possible, adding Murtlap Essence to the water, then I had the elf support his head while I tipped some of the Potion between his swollen lips. There were teeth freshly missing and he hissed with pain as I poured the mixture in.

'Can you hear me?' I asked again.

This time he grunted.

'Look, I'm sorry. I don't know why they've brought you here. They've asked me to fix you up so they can go on with the questioning …'

At that, he opened his eyes. Only, the lids were so swollen that he could not open them properly, he had to lean his head back and peer out from slits. I could barely see enough to tell that his eyes were grey, like mine. The man whispered something, but the words did not make it clearly past his immobile mouth, which had been stretched taut with bruising and blood blisters.

He tried again, and I understood. 'Let me die,' he said.

'I can't.' Whether I was speaking as someone who was providing care, or as a Death Eater, I cannot tell you. Either way, it was not an acceptable outcome.

'Here,' I said. 'This potion will help with the bruising. It will hurt less, and you'll be able to talk more clearly. Drink it down.'

He did, then sat quietly for a minute while I checked for broken bones and internal injuries. There were many. None fatal, on its own, but enough to kill him within a day or so if I left them. It would be a very bad day, though.

'Right, you're not in good shape, but you know that. Why they didn't use Veritaserum I'll never know. Bella definitely has some, and so does Lucius, I gave it to both of them. Stupid waste …'

I was muttering so quickly that I missed his words and he had to repeat himself. 'They did, they did.'

'They what?'

'Used Veritaserum.'

I stopped my ministrations and stared at him. Before I spoke to him, I had the momentary sense to send Malfoy's house-elf from the room. And then, as I knew I should not, I asked questions. 'But why didn't you tell them what they want to know?'

'Because I don't know the answer!' he wailed softly, moving his jaw as little as possible. I realised that some of the sticky mess on his cheeks was tears, amid the blood and crust.

'But why did they keep going?'

'I don't know,' he moaned.

But I did.

I reached for my bag. 'I can't get you out of here,' I said quickly. 'They'll kill me first. But I can make it so you don't feel what's happening. If I say I have fixed your heart and lungs, they'll get back to work. But if I don't really fix them, then I think it will be two, maybe three curses before your heart gives out altogether. It's the best I can do for you.'

'Thank you,' he whispered, and one of his bloody hands reached out to clasp mine, curling his two working fingers around my palm.

'I'm so sorry …'

'Thank you,' he repeated, squeezing my hand with what strength he had. 'Can you tell my parents I'm dead? My name was Benedict Flutterbee.'

'I will. My name is Regulus Black.' It was all I could give him, aside from his death.

This time I mixed hastily. It did not matter if I made a mistake in this brew, in fact, I was rather counting on my actions being put down to overconfidence. Enough bone-mending syrup to keep Benedict in one piece, more Murtlap Essence, a single drop of Asphodel so that it would provide detachment but not obvious stupor, more Blood-Replenishing Potion – too much in fact – and then aconite, a very liberal dose.

I stoppered the vial, and shook it three times, murmuring a magnifying Charm on its qualities.

'Benedict?' I wasn't sure if he was still conscious.

He lifted his head as much as he could.

'There's an awful lot of aconite in here. I don't know if you did Potions at Hogwarts, but aconite – wolfsbane you might have called it – will numb you – your hands and feet first, then onwards, until it reaches your heart. I've set it to work quickly, so it should be ten, perhaps fifteen minutes, not hours. Your mind will stay with you. I've added in something to keep you calm, but you'll be able to think, you'll … you'll be you to the end. It might make you throw up, or void your bowels, I think it should work too quickly for that, but if it does, bugger the dignity, see if you can get some of the mess onto Bella or Barty.'

He made a strange choking sound at that, and I realised it was laughter.

I smiled, and he reached out and took my hand again. 'Are you truthful? Can I really die now? Or is this just another torture?'

'I was a truthful man,' I told him, 'before this war made me need to tell lies. I have not lied to you.' I thought for a moment, then added, 'But I will lie to your parents. I will tell them it was quick, and that you felt no pain.'

'Thank you.'

I held the vial to his lips, and helped him to drink from it, not even asking if he was sure, because that would have been cruel.

'Goodbye,' I said. 'Good luck.'

I went to the door and opened it; the corridor was empty. I could hear voices, and when followed them, they led me to a nearby study. Lucius was sitting at his desk, with Severus on the other side of it and Bella and Barty pacing the floor. All turned to me as I walked through the door.

'Is it done?' Bella asked eagerly.

'He's repaired enough for you to resume questioning him,' I said. 'But nothing harsh, use restraint. He's still terribly weak: any serious hexes will kill him.'

'Of course. Thank you, Regulus.'

I did not miss the smile she exchanged with Barty. Neither did Lucius.

'I will accompany you,' he said, to the dismay of both. 'Regulus, wait for me here. I'll see you home. Severus, if you would be so good …'

'I have nothing calling me away, I can wait, too.'

'My thanks.'

Severus and I were left alone, and I was grateful for it. I had not seen him since the attack on the McCoy house, but he looked well.

'Would you like to wash?' he asked me.

I looked down, and realised that I was covered in Benedict's blood.

'Come on,' he said. 'I'll take you. And I'll also take this bottle of Firewhisky and these glasses, and if we've very efficient we can have all of us back before Lucius notices.'

I smiled my assent, and he led us towards the nearest bathroom. There he let me pour a basin full of water and wash myself while he poured glasses of whisky and insisted I drink one.

'It is a very fine thing for us that you've taken on this role,' he observed. 'But I suspect it is not so enjoyable from your perspective.'

'Some of it is,' I replied. 'Saving you was good.'

'A very worthwhile use of your skills,' he agreed.

'I'm not sure that tonight has been,' I confessed.

'No.'

'What did they want out of him?'

Severus lowered his voice, so I could only just hear him. 'He's from the Department of Mysteries. There is a prophecy, the record of which should have arrived there by now, it tells of the coming of one who can defeat the Dark Lord.'

'Defeat him? But that's not possible!' I stopped myself, horrified at what I had let on.

Luckily, Severus had no idea. 'Even the greatest wizard can be tripped up by fate, Regulus. Happily, fate seems more in our favour than not, for I happened to be there when the prophecy was made.'

'There?'

I had never seen Severus so full of pride. 'In Hogsmeade. I heard it, and have alerted the Dark Lord to the danger. We will identify the one the prophecy speaks of, and destroy him.'

'But then … why did you need the man from Mysteries?'

Doubt flitted through Severus's eyes. 'I did not hear the entirety of what was said … but it will be enough!'

I nodded. 'Thank you for letting me know.'

He smiled conspiratorially. 'I shouldn't have, of course.'

'I will never say a word,' I promised.

'Come on, finish up your drink. Let's get you back.'

I was neat and apparently relaxed by the time Lucius came back from the blood-smirched drawing room. His face was grim and his mood dark.

'Bella and Barty?' Severus asked.

'I've left them to deal with their mess,' he snapped.

'Ah,' said Severus.

'Apparently restraint is not a term they are familiar with. And I do not believe the man knew anything after all. A pointless waste.'

I held my tongue.

'You did what you could,' Severus reassured him. 'We have a great deal of information to go on, the rest will come.'

Lucius looked meaningly at me, and Severus nodded in acknowledgement that the topic should be avoided.

'Come, Regulus, I'll take you home.'

He was entirely calm until we arrived at Grimmauld Place. There, rather than accompanying me up the stairs to the door, he dragged me into the park across the road.

'What in Merlin's name are you playing at?' he hissed.

I looked at him blankly, which was no great trick on my part; terror had driven all thought from my head.

'Give me that!' He snatched my Potions satchel from me and opened it, rummaging until he found the bottle he wanted. 'This was full when I gave it to you!'

He was holding up the aconite.

I took refuge in the truth – most of it at least. 'I used it to dull that man's pain, so those two could go on "interrogating" him. You know as well as I do they were just killing him in stages!"

'Not in my house Regulus!' Lucius dropped the satchel and grabbed at his hair. Holding it in great chunks to the sides of his head, he walked back and forth, hissing between his teeth. After a few moments of this, he came back to himself, took my arms, and dragged me down to sit on the ground with him.

'I have a wife,' he explained. 'I love her very much, and she is carrying my child. Now I understand, I truly do understand, that you did what you thought was best. And I sympathise. In fact, if it were up to me, I would be applauding you. But it is not, and you did it in my house, and you put my wife and my unborn child and my parents and me in danger because you felt sorry for someone who is nothing. Do you see? Do you understand why I can't just look past this?'

I wanted to tell him that yes, I did. But instead, I lied again. 'Did I add too much? It was all such a rush. Are you telling me that I killed him with an overdose? I should have weighed him to be sure …'

Lucius thought for a moment, then tried a different tack. 'Of course, it is good to know that you can kill for our Lord. Did you threaten the man? Tell him that you could make him well or end his life, and that he could choose by whether or not he revealed his secrets to you?'

'I'm confused, Lucius,' I said, and that was true, for I was uncertain as to why he hadn't hexed me yet. 'Did I get it wrong? I wasn't trying to do anything but act as you asked me to. Obviously I've fucked up, but you're talking madness. I've just made a mistake …'

He frowned. 'You're not a mediwizard, are you?'

'No!'

'Just a smart boy with a gift for Potions.'

'Yes! And reasonable basic skills from keeping my Quidditch team in a fit state. That's all I am. I've been studying, all the time, and I've tried as hard as I can, but there are some things I just don't know. Maybe the murtlap and the aconite shouldn't be mixed for someone with his level of internal bleeding, but it seemed as though it would work …'

'I want to believe you …'

I stayed silent, because an innocent man would surely not need to plead his case.

'But I no longer know whether or not I can trust you.'

'Lucius!'

He would not meet my eyes. 'I am sure that I probably can, but it's probably, Regulus. That doubt is there now, and that's fatal.' He reached into his pocket.

I sat, unmoving. I would not fight him. He had a wife, and a child on the way. I could not do that to Cissie.

He pulled a pouch from his robe and gave it to me. 'This is my emergency fund. There are ten thousand Galleons in there. It will be enough to get you anywhere in the world. Just go. Today. I will keep quiet. I will not tell anyone about my suspicions, not even if you stay, because casting doubt on you would cast doubt on Narcissa, and me, and even Severus. But I will make certain you are called on, and I will be behind you on every mission, and my hexes will go astray. Do you understand me?'

I realised that my mouth was open, but no words were coming out.

'I am sorry, Regulus. It is the way it must be. You will find a good life elsewhere. And it's not forever. When the war is over, you may return. Until then, I cannot take the risk that you may turn out to be a liability.'

I closed my mouth and swallowed. 'Right. All right. I see.'

I looked directly at him. 'I will do as I have always done and follow your instructions. I will go away, and it will be as though I have vanished from this Earth. I will not endanger you, nor my cousin, and you will not hear of me again until this war is done. And then you will know that all along I have acted in ways that were for the best, and which should have made you proud of me.'

He reached out and clutched me to his chest, hugging me tightly. 'I know. I know you will. I am proud of you already, Regulus. Until we meet again.'

'Wait …' I handed him back the pouch. 'I have enough funds.'

He took it without pause, gripped my shoulder once more, then stood and Disapparated in one fluid motion.

I felt better that he had taken the pouch: I had feared it may have contained a device to track me, or a Charm to destroy me. A sudden dark thought followed, and I slipped quickly out of my robe and set fire to it. I popped the Potions bag on top of the flame, and encouraged it to burn to ash, too.

Then I ran inside before anyone could see me in the west of London in the early hours of the morning wearing only a vest and breeches.

I did not go back to bed. Instead, I liberated Kreacher from the wardrobe, then dressed myself again, ignoring his questions as to my state of nudity. I snatched up my quill, and one sheet of Black watermark and another of anonymous parchment. On the first I wrote my letter of resignation, thanking Madam Jones and informing her I was committed to travelling abroad for family obligations. On the other, I disguised my writing to send the news of Benedict Flutterbee's death. I was short, but I hoped kind. My last words were that he had been incredibly brave.

The Ministry opened at six, though only a handful of staff were ever there before sunrise. That morning, I was one of them. I shoved the missive concerning Benedict into an Internal Mail chute, then made my way to the library.

I had brought two things from home. The first was an Elizabethan pillow, goldwork over red silk, which I placed on Madam Jones's desk, my letter atop it. If she could no longer rest as long without her assistant, she could at least rest more comfortably. The second was a mokesin pouch, which I filled with books, shrunk to fit. I felt badly for stealing, but in all honesty, the library was safer if these books were not available.

Then, as dawn began to threaten, I went home. I took off my boots and tip-toed carefully into my parents' bedroom. I went to the right side of the bed, and shook my father's shoulder gently.

'Father?' I whispered.

'Regulus? What is it? Don't wake your mother.'

'I won't. Father, I need your help.

He never once said that he had told me so, never once shook his head at my stupidity. Rather, he helped me pack what I would need, and made excuses with Mother for why the two of us were going for an early morning walk. We made it round the corner before he grabbed my arm and Apparated me a mile and a half east.

He pulled a note from his pocket, and showed it to me, and with that a house appeared before me, narrower than our home, but just as well built. He bustled me inside, to a well-lit and spacious entrance hall.

'Where are we?' I asked.

'It was my Uncle Regulus's,' Father explained. 'He left it to me, I always meant for you to have it. It's as secret as home, more so, since none of your friends know about it.'

I thanked him, and he held me, and told me that I had to be careful. 'Stay inside, no matter what. The house comes with an elf, Welky. He's old but devoted, and very useful. If you need anything he cannot supply, send him to me. Not your mother, I am going to tell her I've sent you to Botswana.'

I laughed then, because that was one place that had never occurred to me.

'I can't lock you up,' he said. 'But be sensible, my son. You're all I have left, and you were always my favourite.'

He knew. I am sure that even then, he knew.

'Father, when the war is over, if Sirius comes back … he was always kind to me. Even in the last few years, he has always looked out for me.'

'We'll talk about that when the time comes,' he promised.

And so he left me here, and I unpacked my bags, and took possession of a house that was far too big for me and a house-elf who was happy to be called on only at mealtimes and I set about reading and planning.

After two weeks, I had read everything that I had smuggled from the library, and I had learned several important things. The first was that there were spells that could render fluids unable to be drained by any method save that set by the wizard who bespelled them. The second was that house-elf magic could only create the tiniest amount of fire: enough for a warm study, but not the conflagration I would need. The third was that in light of the first and second things, I would not live to see Christmas.

I was tremendously grown-up about my third realisation. I sat down and calmly wrote letters first to my Father and Mother, and then to Sirius. I tidied my books, left a note asking that they be returned to the library after the war, and ate chocolate for breakfast as I decided that tomorrow would be a good day to get Things Done.

It was only two in the afternoon by then, so I read the first and last chapters of several mystery novels I had been hoping to get to, did several laps of the house to keep myself in shape, and then tried to decide whether it made more sense to die in my best robe or my worst one.

And by then the sun had well and truly set and the darkness began to seep in through the windows and I told myself it was a terrible idea, but really it was that or lose my bottle entirely and leg it for Botswana, so I grabbed my quill and a square of parchment and I called Welky in and asked if he could get a message to someone without anyone else seeing him, and he assured me that he could.

And so I wrote to her. Regulus Black lives at 14A Eaton Square, it said. Underneath that, three stark words: Lily, I'm afraid.

She came.

Welky had barely returned when I heard the knock at the door, and I ran for it, assuring him that he would not be needed and that he could have the evening off. He checked that I was sure, then Disapparated happily, and I opened the door.

Lily had her wand drawn. She was wearing a Muggle coat and a blue woolly hat. 'Are you alone?' she whispered. I nodded, then quickly collected the hat in my nose and her wand in my back as she barrelled into me, hugging me more tightly than I would have credited given the look of her arms.

She pushed me inside and shut the door behind us. 'Never again!' she said angrily. 'I don't care what your reasoning is, you never again entirely disappear for this length of time without sending word. And you certainly don't send word like that! I was all set to Apparate to Sirius's and come back with the entire Order!'

'I missed you, too,' I said, smiling.

'Prat. Make me a cup of tea. And you'd better have cake.'

I did. Three types. She had taken off her coat and hat and was sitting on the settee when I came back in with the tray.

'So,' she began. 'What trouble are you in and how can we get you out of it?'

'Both good questions,' I said, cutting her a slice of the chocolatiest cake. 'Quite big trouble, and I am afraid there's nothing for it but to plunge deeper in.'

'Regulus Arcturus Black, what have you done?'

She did not sound the least bit like my mother.

'Where did you learn my middle name?'

'I asked your brother. He likes talking about you. Keeps hoping you're going to turn up on his doorstep asking to be taken in.'

'I nearly did.'

'Do! He'd be thrilled. Excellent cake.'

'Thank you.' I decided to dive right in. 'Lily, I think I know how to defeat Voldemort.'

She laughed.

'I'm serious.'

She stopped laughing. 'Really? Really? Well, why are we eating cake? We'll take it to the Order. We can mount an attack.'

'That's the thing.' I put my cake plate down, and waited till she did the same with hers. 'I've looked over it from every angle, and it's a one-person job.'

'All right. Well, you explain what needs to be done, and we'll find the best person for it.'

'No. Lily, I've thought it through at length and the best person is me.'

She nodded thoughtfully. 'Because you're an insider and can get in and out without detection?'

'In,' I agreed.

She noticed. 'What about the out?'

'Fairly certain there won't be an out.'

'Well that's not acceptable.'

'But it's what needs to happen.'

'No.' She pushed her hair back from her face. 'No. You're thinking like your brother. You're a young man who hasn't done anything yet. There are other people who are able to make sacrifices, who are older, and have less to lose, less to miss out on.'

'Lily, I'm not going to ask anyone else to do this.'

'You haven't even told me what "this" is!' she snapped.

'No. And I'm not going to.'

'Fine. You're being ridiculous. I'm going.'

She picked up her coat and hat and stood up. Then she flung the garments back onto the settee and came to my chair and punched me hard in the arm.

'Stop it,' she ordered. 'Get over your Great Heroic Statements for a minute and tell me what you're going to do and we'll find a way to make it survivable. There's always another way.'

'That really hurts.'

'Good.'

I reached out and caught her hand before she could punch me with it again. 'There's a prophecy. They know there's someone who can defeat Voldemort. He's coming, whoever it is.'

She uncurled her fist, and curled her hand around mine. 'How do you know?'

'Severus heard it. He didn't give me any details, only that, whoever this wizard is, he's expected. They tried to learn more from a man who works where they keep the prophecies, but he didn't know anything. They killed him.'

I stopped, then went on with the truth. 'I killed him. I gave him a potion that stopped his heart. He asked me to. But even then I lied and told him he'd die from their curses, so he would think of me as someone who took away his pain and not his life. He had maybe ten minutes left, and I just wanted him to think well of me in them.'

I looked up and saw Lily was crying.

'I know,' I said. 'If there had been anything else I could have done … But all I could do was make it easy for him. And fast. They are scared, Lily, scared of this wizard and already actively working against him. When it becomes clear who it is, you will all be needed to keep him safe.'

'But what does this wizard have to do with you?'

'Voldemort has a back-up plan. I know the details of it, and I've worked out how to thwart it. Aside from the fact that it's almost certainly lethal, my plan is excellent, and should guarantee the wizard in the prophecy will be successful.'

'But … when? When is this mystery wizard meant to get here? How are we even meant to know who he is?'

'I don't know. It could be tomorrow, it could be a year from now. But that's why I need to act quickly.'

'How quickly?'

'Tomorrow.'

She let go of my hand and returned to the settee. 'No. You're being ridiculous. You're upset because you killed someone, and I won't pretend that's not awful, but you did it out of mercy, and that's much less awful. You can't bring him back by killing yourself, that's absurd.'

'The two aren't connected,' I protested.

'Of course they are.'

'Well, yes, but only because I found out about the prophecy because I was there for him. Don't you see, Lily? I'm the only person who has all the pieces, and I'm also the most expendable.'

'Don't you dare say that!'

I jumped a little at the vehemence of her shout. I think she surprised herself, because she covered her mouth with her hand for a moment, but then she went on.

'Don't you dare. You're not expendable, none of us are. That's the way they think. We think about saving everyone.'

'Lily, I'm one of them. So let me do this, so I can save all of you.'

'Let you? What choice are you giving me?'

'None,' I admitted. 'But until I told you what I was going to do, I didn't think I would be brave enough to really do it.'

She thought for a moment. 'You said almost certainly lethal.'

I nodded.

'How almost?'

I shrugged. 'From what I know, and from what I've researched, I can't see a way in which it's not going to kill me. But I always like to consider the possibility of a miracle.'

'Do you believe in miracles?'

'No. But if one were to present itself, I'd happily change my mind.'

She smiled at that, then shook her head. 'I wish you'd never told me.'

'I know. I'm sorry, it was cowardice on my part. But I'm feeling braver now.'

'Regulus, I'm being serious, tell me what you know. You're the only person who's looked at the problem, other people will have other solutions.'

Now I shook my head. 'If you know, and Voldemort finds out you know, he will destroy you. This is his great secret, Lily, the one he would kill everyone to keep. The only reason I am still alive is that Lucius Malfoy thinks I am a soft-hearted coward, because if he had exchanged one word of his suspicions with the Dark Lord, no unplottable address would be enough to protect me.'

I moved to sit beside her on the settee. 'Anyone I tell the details to, I condemn. But I wanted you to know why I died, so that you would not think I had just left. And so that one day, you could tell Sirius, and let him know that I died trying to do the right thing. If I'm successful, you'll know what it was by then.'

She took my hand, but did not speak. Only looked at me, shaking her head slowly and biting her lip.

I forced a smile to my face. 'Anyway, now that I've made you thoroughly miserable, you should probably go back home. Won't Potter be worried?'

'I told him I had a letter from my sister and that I had to go to hers. He'll never ask her, they hate each other. Your house-elf appeared at just the right time for the late post round our way.'

'Oh,' I said, surprised at her easy facility for lying, which was absurd, since how does anyone survive a war without a gift for falsehood?

'I said I might be all night, so there's no rush.'

I was suddenly very conscious of her hand in mine, and let go of it, returning to my chair and my abandoned tea and cake.

'Very good cake,' I muttered, taking a sip of tepid tea.

'If you do this,' Lily said, 'you will die without ever having gone anywhere. Sirius said you've never even left the country.'

'Does Wales count?'

'No.'

'Well, I've read books. And Mother always said Foreigners were just like us, only less so.'

'You've never had your heart broken. You've never even had sex.'

'Steady on!'

'You're letting all of that go. All the futures that you could have had. All gone.'

'Perhaps that will make up a bit for the past.'

'Your past is not that bad! Certainly not compared to others!'

'None of them want to make amends, Lily.'

She flopped backwards, her hair contrasting violently with the red velvet of the settee. 'It's just a stupid bloody waste.'

'Yes. That I agree with.'

'Stop eating cake, Regulus. You're upsetting me.'

I put the plate back down. 'Sorry.'

'And stop saying sorry.'

'All right.'

'And stop letting me boss you around.'

'Can't, I'm slightly afraid of you.'

She laughed at that. And then she looked at me, long and hard, until I was forced to look away. When I looked back, she was taking off her boots.

'What are you doing?'

'Finally working out what all those old ladies at the Women's Institute were always on about. And it's a terrible cliché, but it is the right thing to do.'

'None of that made any sense to me.'

'No, I don't expect so. Come on.'

She got up and padded over to me, barefooted, took my hand and pulled me up out of my chair. Then she led me out of the drawing room and along the corridor, pushing open doors as we went until we arrived at my bedroom.

I began to make out a possible meaning as she led me inside.

'You should go home,' I said. 'It's awfully late.'

Lily shook her head and let go of my hand. 'It's not late at all,' she said. She reached into her pocket and took out a hair elastic, drawing her locks up into a ponytail. 'It's New Year's, the end of 1977. I've had a fight with my sister and gone back to Hogwarts. You were so lonely without Sirius that you came back early, too. The teachers are all mostly pissed and we're alone.'

She took off her ring and removed her earrings and put them on top of my dresser by the door. 'I'm not going out with James yet, and I haven't had my ears pierced. We started talking over dinner, and you're showing me the Slytherin dormitory.' At that, she reached out and took my hand again.

'Severus would be here,' I whispered.

'No, his parents have made up. He's having the loveliest holiday ever, he's happy.'

'He's happy,' I echoed, and she raised my hand to her jaw. I moulded it around her fine bones and sank my fingers into her pulled-back hair.

'You had a bottle of Firewhisky, and we took a little each, feeling awfully daring. And then you told me that you thought I was beautiful, and I told you that I thought you were, too, and now you've decided to be tremendously brave and kiss me.'

'Now?'

'Now,' she breathed.

It was not like the time I had kissed her at the Ministry. This time she met me with eagerness, pressing her body against me as her lips gently parted and I learned the warm taste of her. I dropped my free hand to her waist, and hers went to my face, then to my neck, unbuttoning my robes. Her fingers were cool and nimble as they darted inside the wool and traced the lines of my neck and collarbones. I shivered, and felt her lips turn up against mine. Then they moved to my jaw and my throat, and I saw her hair ruffle as all the breath left my lips in a long sigh.

She moved a little away from me, took my hands, and brought them to the belt of her dress.

I blinked at her in surprise, but she nodded.

I was tempted, almost impossibly, but I kept hold of her hands. 'Lily,' I reminded her. 'You don't really want to.'

She kept her bright eyes on mine. 'It's Evans, Black, and I do.'

'But …'

'No, it's nearly 1978, and there are no buts. There are no reasons not to. Just the two of us and a near-empty school.'

'It's Belgravia, 1979,' I corrected her.

'Then you're remembering this,' she insisted. 'This is what happened then.'

'Lily …'

'Regulus, please … It's what I wish I'd done …'

'You love James.'

'Yes. But I didn't then. This could just as easily have happened.'

'But it didn't.

'Then let it happen now, and let's pretend it happened then.'

And I was out of arguments, and my fingers had already left hers and undone the knot of her belt and started on the buttons that ran down the front of her dress. There were a ridiculous number of them, and I fumbled, but finally I had it opened to her hips, and she shrugged her way out of it so that it fell lightly down to the floor.

Beneath it, she was wearing only light Mugglish underthings, and I held my breath at the sight of her skin. It was all over that soft cream, with smatterings of freckles on her chest and shoulders. I paused to kiss her again, and to take the elastic from her hair. I ran my fingers through the long red strands, and my hands came to rest on her shoulders. Bold now, I pushed the straps off them.

'There's a hook, at the front,' Lily whispered.

I undid it with only a moment's clumsiness, then sighed as the garment fell back and down her arms. Her breasts were beautiful, small, yet surprisingly full. She smiled encouragement, and I moved my hands to them, marvelling at the way they fit within my palms, and the peaks at their centres.

She shivered, and I wrapped her in my arms to warm her up. And I kissed her again and I tried to reassert a modicum of common sense – because somebody had to and apparently it wasn't Evans.

'Thank you,' I murmured into her hair. 'This is more than I ever hoped for. But my death is not a good reason for you to sleep with me.'

'No,' she agreed. 'But the fact I desperately want to is.'

I did try for common sense, but there were limits.

She reached behind her back and took my hand and guided it down towards her knickers. They were a flimsy scrap of green fabric, not at all like the long white cotton I had been told good witches wore. I pushed downwards, and gravity helped me after a moment and then Lily Evans was standing bare before me and I wanted to say stupid things, but thankfully was incapable of speech, and she reached up and undid the remaining buttons of my robe.

I swear that I didn't plan it, but I had been entirely inside the house all day, and had not bothered to put anything on beneath, so when she pushed the wool back from my shoulders and it fell to the ground, it was like the unveiling of a rather poor statue.

Appallingly, my already erect prick chose that exact moment to twitch upwards. I might have died of embarrassment, but that Lily's soft hand reached out and encircled it tenderly.

She smiled. 'I knew you'd be beautiful. All over.'

And because she said it, for that moment, I was. I lifted her up, which made her laugh, and I meant to carry her to the bed, except I tripped, so it was sort of a stagger, which ended up with me sitting on the bed's edge and her in my lap, but it was better than the floor and no one sustained any damage.

I had a moment to feel the astonishing luxury of her skin against mine, and then she stepped nimbly out of my lap, and then across me, with one knee either side of my legs. She pushed the two of us back a foot, so that she was straddling my lap and I was marvelling at all the beauty I held in my arms.

I kissed her, long and deep, and ran my hands over her skin, learning the contours of her back and hips, the slight roundness of her arse, her long thighs and the place between them where she put up with my reverential fumblings before reaching down and moving my hand to her hip, then guiding my prick home.

And my right hand was never like that – soft and elastic and wet and warm. She moved against me, once, twice, and then I was no longer able to count as my body shuddered into a release that it had known too few times and never with another person. I gasped my joy against her hair, then dropped my face to her shoulder to hide my mortification.

She kissed my neck tenderly and whispered my name, and after a moment I looked at her. 'One thing that I have learned through being friends with your brother,' she said in the gentlest of voices, 'is that every man's first time is really quite fast.'

She ran her hands the length of my back, then went on. 'Of course, I am also friends with Remus, who said that what Sirius meant was every man's first, third, sixth through ninth times, not to mention when drunk, or just lazy, were all better measured in seconds.'

I couldn't help chuckling, and could feel my laughter echoing through her body, making her shoulders vibrate beneath my hands, which was at once the strangest and most intimate sensation yet.

'So,' Lily said, kissing my jaw until I turned my head and she could reach my lips again, 'it's just as well you're young, so we won't have long to wait for your second time. And I am fairly sure we can test Remus's theory on the third, maybe even the sixth through ninth if we pace ourselves.'

At that, I felt a throb of life in my cock.

Lily smiled. 'There we go.'

As it turned out, Remus was right about the third, but wrong about the sixth.

I expected her to be gone when I woke up. But in the thin grey hours before dawn, she was still in my arms, breathing warmly against my chest. She had invaded all the boundaries of my person, I even tasted and smelled of her, and I was startled to find it delicious rather than a little disgusting, as I had always thought it would be.

We had made use of the night. Just before eleven she had let me run my hand down through the soft thatch of red hair between her legs and taught me what to do for her, which was a joy to watch, and repeat. She had pinned me down a little later and taken me in her mouth, which made me want to know the taste of her, too, so I grabbed my wand and levitated her, to shouts of laughter, and then gasps of more private delight.

We did not want to sleep, but were too exhausted not to.

Now, in the light that might have been the moon but was more likely streetlamps, I memorised her limbs, and the cluster of freckles on her left shoulder, and the way her hair did not lie flat against her skull at one point at the top of her crown.

She stirred, and looked up at me blearily. 'Morning,' she said.

'Not quite yet.'

'Can I have a glass of water?'

I summoned two, and we sat up in bed to drink them. We moved slowly, with tired muscles that were not yet awake.

'When are you going?' she asked.

'Later. Quite a bit later. You?'

'A little before that.'

She put my water back on the side table, too, then kissed me and nestled into my arms. 'That was all quite astonishing,' she said.

'I can easily say it was the best night of my life,' I replied. 'And ask that you ignore the low baseline it's compared against.'

She laughed. 'I didn't know you had a sense of humour.'

'I don't, normally. You bring out the best.'

'I'm glad. I'm glad I met this Regulus.'

'You don't regret it?'

'Not one moment.'

I held my breath before I asked my next question. 'Do you regret that the real 1978 didn't begin like this?'

She looked up at me. 'Yes.'

I was learning to read her face now. 'But you don't regret that you fell in love with James.'

'No.'

'Are you happy with him?'

'Very.'

'Could you have been happy with me?'

'Just as much.'

'Oh.'

She smiled. 'There are Muggle scientists who say that there are many worlds just like this one, all separated by one different decision, here or there. I think that in many of them, you spoke to me in 1978, and when Lucius Malfoy came calling for you, you were busy with me. We'd be getting married about now in those worlds, you'd have been out of school long enough for me to not look like an awful cradle robber.'

'I'm not that young.'

'You're a baby.'

'Do some of those worlds have no Voldemort?'

'Many.'

'Then there are some where we grow old together.'

'I'm certain there are.'

'That's good to know. Some version of me should have lots of nights like that one.'

She laughed, tiredly but properly.

I thought of something. 'Lily?'

'Yes?'

'You and Potter are bound to have children at some point, aren't you?'

'Yes.'

'I was going to say this to my own wife, but I'll tell you instead. Give them new names, not ones that belonged to dead relatives. I was named after my great-uncle, and this is his house. It's a little bit creepy. Stick them in as middle names if you can't resist.'

She was laughing, but I was serious.

'All right,' she said. 'I promise. Only new names. And with a bit of luck, the war will be over soon enough to use Regulus as a middle name for one of them, because everyone will know you died a hero by then.'

She kept her voice level, but her hands tightened their grip on my arms, and I bent to kiss her, and to tell her it would be all right, even if it wouldn't. And she stretched out against me, warm and lithe, and I forgot what I was going to say.

Remus was wrong about times seven through nine, too.

I tried to stay awake. The sun was pouring in through the windows now, and I could see the green of her eyes as she watched me struggle against sleep.

'I have to go soon,' she said.

'I know.' I sat up to help clear the muzziness of my thoughts. 'I want to say something, and I want you to know that it's not something new, it's something that's been true for a long time. I love you, very much.'

She kissed me, and she smiled, and she said, 'I love you too, Regulus.'

'And you also love Potter.'

'Yes.'

'In a slightly different but really quite similar way.'

That made her laugh. 'Yes.'

'That's good. He's a good man. He deserves you.'

'So do you,' she whispered.

'Yes, but with him you will have a life.'

She didn't answer that, because there was nothing to say, but she held me until I went to sleep, and I dreamed of her arms and the sound of her heartbeat.

When I woke up again, it was still early. She had gone, as I knew she must, but she had left every sign of her presence from the extra glass to her scent on the sheets, to red hairs on the robe I had been wearing.

I savoured them, like the late autumn sunlight that bathed the balcony as I took breakfast. Although I had named today as the day, I saw no need to rush. It was a beautiful day, and the work I have to do is the work of darkness … and perhaps I also wanted to live a little with the memories of last night.

So I sat to write. That was at the start of the day and now it is near the end. I will give the papers to Kreacher and ask that he give them to Lily when the Dark Lord is defeated, so that she can know how she made it possible. And, if I fail, that he hide them away, so that Lily need never explain.

It's probable that no one will be able to read any of this at all, since I've written so hastily and poorly. She took my favourite quill, the Everlasting Sirius gave me for my eleventh birthday. I like to think that she will chew on it absently where I did, that her lips will be where mine were.

I've not washed, and I know that is perverse, but I do not care. Lily has given me strength. She has taken a token to keep me with her. I have the knowledge of her courage and the memory of her skin against mine. It will be enough to carry me through what must be done.

It is fully dark now, and so I will finish here, and write one last note before I lay down my quill and call for Kreacher. I will make a final journey, and strike a blow without ever knowing whether or not it hits home. But I believe it will. And Lily will be safe. And she will remember me.