The shattered pieces of a tea set lay on the dungeon floor. A handle stuck up incongruously from half a cup. The teapot, fatally cracked, leaked dark tea like blood into the gaps between the flagstones. Only the spoons, silver and shiny, lay undamaged in the wreckage. The boy stood in the midst of it all, seventeen years old and full of the sudden hot anger of youth. Professor Slughorn was leaning against the sideboard, wringing his hands as he surveyed the carnage. 'Oh dear, oh dear, oh dear,' he murmured to himself.

The boy turned to his teacher, face working furiously. He dragged the words from deep inside him, one at a time. 'This – is – all – your – fault! You promised me! You promised!'

'My dear boy…'

But the youth wasn't listening, he was pacing again, full of the same angry energy that had resulted in the room's destruction. 'There's got to be a way to make this better,' he muttered feverishly, black eyes darting. 'Got to be. It can't end like this, it just can't. There must be a way.' He rounded suddenly on the Professor with a gasp. 'Time Turner! That's it! You've got to get me a Time Turner, so I can go back and stop this happening.'

Slughorn backed away a step or two, holding up his hands as though to fend off an attack. 'My dear boy, even if it were possible for me to furnish you with such a thing – which it isn't – it wouldn't work. Time Turners don't work that way!'

'Yes they do!' shouted the boy, coming closer to Slughorn than the teacher liked. 'They have to! OK? I won't let this happen, I have to find a way!'

'You can't change the past!' cried Slughorn, gripping his wand and hoping he didn't have to use it against a student. 'I did my best, Severus, I really did. But some things can't be undone. Some things are just… inevitable.'

'Inevitable?' Severus repeated, staring at the Potions master with that alarming intensity he had. For a moment, Slughorn thought the boy was going to do him some harm, but then the youth turned away and slumped down at the table. 'Yeah, I guess it was inevitable. Inevitable that everything would work out just rosy for stupid Potter, and I'd be left with nothing.' The anger was draining out of him now, but the bitterness in his voice was just as disturbing in one so young.

'Come on, now, Severus. You've hardly got nothing! You're a clever boy, with lots of talent, a promising career ahead of you. In less than a year's time you'll be out in the big wide world. These little troubles seem so enormous at school, but they come to very little in the grand scheme of things. You mustn't take things to heart so.'

The boy showed no sign of having heard, continuing to speak to the table. 'No. She's chosen her path. I thought she was different, special. But she ended up getting taken in by Potter and his cronies just like everyone else.' He took a deep breath. 'It's too late now. You're right about that. It's all too late.'

Slughorn ventured a nervous pat of the boy's angular shoulders. 'You're a good boy, Severus, I've always said that. No matter what they say. A good boy. I know you'll choose your own path, not get led astray by anyone… You wouldn't let that happen, would you? You've got a bright future to come! Focus on that.'

Severus stood suddenly, his foot catching on the china debris. He looked rather surprised to see it there. 'I know what I need to focus on,' he muttered darkly, turning to leave the room.

The Professor tried to stop him, moving his vast bulk with surprising speed to block Severus' path. 'Now, Severus, let's talk about this properly over a nice cup of tea. I'll just have to mend the tea-things…'

'No,' said Severus, with a force that stopped the teacher's fussing. 'There's no point in more talk, Professor. Like you say, it was inevitable, doomed to fail. Talking won't change a thing. Please, just let me go.' And he was gone, slipping past and out into the chilly dungeon corridor.

Horace Slughorn remained still and speechless for several moments after the boy had left, staring after him as though wondering whether to give chase. But eventually he turned away, repairing the teaset with a single wave of his wand. He addressed the photographs on his office wall, a habit he'd found himself getting into lately. 'I did my best,' he told them. 'I tried. I did try,' he said again, rather defensively. 'Maybe the boy's right though. Maybe it is too late.'

'If you had a Time Turner and could go back and change just one thing in your past, what would it be?' Severus asked the question to the blue sky. It was an unseasonably warm April in his fourth year at Hogwarts.

Lily Evans turned her head slightly to look at him, and he felt that tightening in his stomach that he couldn't quite explain. Her face was very close to his when they lay side by side like this, as was their habit. It would only take the smallest, slightest movement and his face would be touching hers. 'I don't think that Time Turners work that way.' She spoke softly, but he could feel her breath on his face.

'Yes they do,' he replied, feeling a little flustered.

'No, I'm sure they don't. Otherwise people would be going back and changing things all the time.' She smiled, and turned to look up at the sky again.

Despite himself, he scowled. His face settled easily into the expression, as though that was its default setting. Severus did not like being corrected, even if it was by his best friend. 'Who says they don't?' he asked sharply. 'Anyway, I'm not saying it's possible. It was merely a hypothetical question.'

Lily frowned slightly, and he felt another surge of emotion. 'I don't know,' she said thoughtfully. 'I suppose it would be something around Tuney.'

His scowl redoubled and he turned to look at her sharply, irritated. 'What d'you mean, Tuney?' he asked, unable to keep the contempt out of his voice.

'You know, my sister. I'd go back and change things so that she wasn't so hurt by me going to Hogwarts and all. I'd make it so we could still be friends.' Lily sighed, and plucked at the grass.

'You're better off without her,' grumbled Severus huffily.

'Let's not argue about this again. It's too nice a day.' She sighed and stretched out further on the grass, wriggling her bare toes.

He conceded with a grunt, but continued to feel piqued. He wasn't interested in the niceness of the day. Unlike his fellow students, he didn't get overcome with an urge to be outside every time the sun shone. He'd have far rather met up inside, in the library perhaps, or the Owlery at a stretch. The brightness of the sky was making his eyes hurt, and the grass was irritating his nose. But Lily had wanted to come outside, and Severus could never resist Lily.

After a few moments Lily asked, 'So what's yours? What would you go back and change?'

It was a question he'd been turning over in his mind for several days, ever since he read about Time Turners as part of a Charms project. The thing he'd most like to change would not be in his gift to alter even if he revisited the moment. He could return to the time he and Lily were Sorted, but there was nothing he could do to get the Sorting Hat to place her in Slytherin. If there were, he would have done it at the time. Unless he could learn a really strong Confundus Charm and use it on the Hat…

Of course, the alternative would be to go back to his own Sorting and request Gryffindor. But he balked at the thought, even if it would mean being in the same house as Lily. The idea of not being in Slytherin was bad enough, but his sense of house loyalty was truly horrified at the notion of being in Gryffindor. Not to mention that sharing a dormitory with the odious James Potter was his exact vision of what hell was like.

He needed to reply to her, so he gave his other preferred option. 'I'd go back to before I was conceived, and I'd kill my father.'

She sat up suddenly and half turned, propped on one elbow. 'You'd kill your father? Why?'

'Because I hate him.' It seemed obvious to him.

'But if you killed your father, you wouldn't exist!' pointed out Lily.

The horror in her green eyes gratified him. She was imagining a world where Severus Snape didn't exist, and she didn't like it. He enjoyed her dismay, although it was misplaced. He hadn't intended to imply he wouldn't exist. In his fantasy Severus still existed, much the same except perhaps a little better looking, but with pure unsullied blood in his veins and a brilliant wizard father. Still, he wasn't going to disillusion her now. He gave a little shrug. 'Maybe that wouldn't be such a bad thing.'

'Of course it would!' she responded warmly, fully turned towards him now, leaning over anxiously. 'It would be terrible, especially for me. What would I do without you? You mustn't think like that, Sev. What's at the bottom of all this? Is it Potter?'

'I can handle Potter,' he muttered dismissively, keen to keep the topic on himself, not his arch-rival.

Lily continued as though he hadn't spoken. 'He's a bully, Severus, a stupid pig-headed bully. Him and Sirius Black – I hate both of them! They think they're so great, they've got no idea what it's like for people like you and me. They don't know what it's like to have Muggle parents that don't understand anything about your life anymore, or a sister who doesn't talk to you because you're a witch, or a Dad that hates magic and shouts at your Mum all the time.'

Severus sighed heavily and turned over away from Lily. He found a piece of twig and began to stab the ground with it. He wished that Potter and Black would just vanish from his life. He wished everyone would vanish from his life, leaving just him and Lily, alone in the world together.

'Sev? Look at me. Please?' He rolled back to face her. She looked serious, which didn't suit her. Lily had a face that seemed to smile even in repose. 'Promise me you didn't mean it? You wouldn't really go back and kill your father, would you?'

He shrugged. 'Not if you don't want me to,' he replied, finally. 'Anyway, you said Time Turners don't work that way.'

'That's not the point, Sev. I can't bear you thinking that the world would be a better place without you. You know that's not true, don't you?' She gazed at him earnestly. Her concern seemed to emanate from her in waves, and he felt giddy with it.

Uncomfortable, he began messing with the grass again. 'No, if you say it's not,' he muttered.

He could tell she was exasperated, and for a moment he thought she'd pursue the matter, but she must have thought better of it. 'You know how I feel,' she said eventually.

But that was just the problem. He didn't know how she felt, and he was too afraid to ask.

The hypothetical questions game started early on in their friendship, the year before they started Hogwarts. Severus fascinated Lily, and not just because of his claims about wizardry. His very oddity seemed to back up his story. He certainly didn't seem like other children she knew. Of course, Lily was later to discover that Severus wasn't much like other wizard children either, but by that time they'd forged too close a bond for it to matter.

Lily would ask him endless questions. Is 'hocus pocus' really a spell? Does the Queen know about magic? How many witches and wizards are there? How fast can a broomstick go? No matter how obscure or complicated the question, Severus had the answer.

At first she hung on his every word, believing anything. But Lily was bright, and as time went on she began to suspect that Severus' answers were often flights of imagination. She didn't mind, and began to make up more and more ridiculous questions, just for the pleasure of hearing his inventive responses. That was how they came to the point of asking purely silly 'what if' questions of each other, giving the answers as much care and consideration as they would the responses to their eleven plus exam.

Learning about Severus himself was rather harder. He was not someone who easily gave up personal information, and his thin, scowly face was often hard to read. At school they were in different classes and their paths never crossed. She had never even noticed him before he arrived in her life on that day in the park, eager and awkward and full of stories of her being a witch. And she quickly realised how she'd missed him – Severus was an expert at making himself small and invisible. But once she started looking out for him, she often would spot him, skulking in shadows and avoiding eye contact with anyone.

It was an unlikely friendship, and one that was bitterly resented by Lily's older sister. Petunia disliked Severus, sensing from the very start that he represented a threat of some sort she couldn't quite explain. For a couple of years she had been growing increasingly alarmed at some of the odd things Lily seemed to be able to do, although it didn't stop her from trying to do them herself. The Snape boy with his tales of a secret world of wizards made it much harder to ignore her fears that her beloved sister was somehow not quite right.

They began to quarrel about it, Petunia pointing out Severus' many faults – his weirdness, his unkindness, his disreputable family, the hungry obsessive look in his eyes. Lily however insisted that Severus was all right when you got to know him, and that his 'weirdness' was due to his exciting double life as a wizard. Petunia huffed off, pointing out they had no reason to believe he was any such thing as a wizard, and she bet that Hogwarts didn't exist at all.

But Hogwarts did exist. One July day, Lily rounded the corner of Spinners End, her hair flying behind her and cotton dress flapping around her legs. In her hand, held high, was an old fashioned piece of parchment covered in green ink. Severus was already on the road, heading in the opposite direction, and gave a yell of delight to see her. He too was brandishing a letter. 'It came! It came!' she squealed when she was near enough, and flung her arms around him then and there.

More excited than she'd ever seen him, Severus grabbed her letter, devouring the contents, even though it said the same as his own. Lily continued, 'A teacher from the school brought it last night, Professor McGonagall she was called! She was like proper witch, with a tall black hat and everything! Though she was wearing normal clothes when she arrived…'

'Muggle clothes,' Severus corrected her. He hated the word 'normal' being used to describe Muggle things.

Lily poked out her tongue, but was too excited to argue. 'She had my letter, and explained all about magic to Mam and Dad. I felt quite sorry for them, they were so surprised. She did some magic to prove it – she turned the coffee table into a chicken and made the teacups flying around the room! – then she asked if they'd noticed anything odd about me, if strange things ever happened, and Mam said about that time Tuney broke my favourite cup by accident and in the morning it was back in the cupboard good as new. So then McGonagall explained about Hogwarts and so on, and they said they'd have to think about it, and they talked all night – at least till I went to sleep – and this morning they said that if I wanted to, I could go!'

'And you do want to?' he asked, looking up from the letter in alarm.

'Of course I do, silly! Who wouldn't want to go and learn to do magic? Tuney was a bit funny about it though, she's shut herself in her room and won't really talk. I think it's a bit of a shock for her.'

'Yeah, a shock that I was right and she wasn't. I'd love to see the look on her stupid face right now,' said Severus, his eyes glittering with malicious pleasure.

'That's not very nice, Sev,' Lily chided him. 'But it's so exciting! I can't wait to go – I can't believe we have to wait fifty-eight whole days until September 1st! Oh – but before that, Professor McGonagall is going to take me and my parents to the wizard shopping place to buy my school things. You have to have a cauldron and robes and all sorts of weird stuff. I wanted to go right away but I'll have to wait until August.' She pouted momentarily, then having spilled out her own story asked rather tentatively, 'What did your Dad say?'

Severus pulled a face, then did quite a good impersonation. 'Bloody owls flying round, what'll the neighbours think? If that thing's crapped in my living room Eileen, there'll be hell to pay.' The boy shrugged. 'Anyway, Mam said I should make myself scarce for a bit. Let's go to the park.'

The summer passed in a happy blur. Lily told her friends she'd won a scholarship to a boarding school. Severus didn't have any friends, so had no need for a cover story. The two children played together often, at least twice a week. Severus would have happily spent all day every day with Lily, but she often went to see girlfriends, and Severus knew he would not be welcome to tag along even if he'd wanted to. So he made the most of what he could get.

One sultry August evening, they were sitting on a wall in their favourite haunt, a quiet place in the crumbling red brick shadow of the old mill. 'If you could have any famous person as your brother or sister, who would it be?' Lily asked him.

Severus looked alarmed and wracked his brains for famous people. They had no television or radio at home, and he heard the names of popstars and sportspeople mentioned at school with no comprehension. Then a name popped into his head, and he blurted with relief, 'Merlin!'

'Merlin? Is he real?' Lily's green eyes were wide.

'Of course – well, he's dead now, but he was real. He was the most powerful wizard ever known, and he could travel in time, and he was so famous that even Muggles today know his name.' He smiled, proud of his knowledge, gleaned from the card that came with the Chocolate Frogs his mother had once secretly brought him in one of her better moods.

Lily shivered with delight, swinging her skinny legs. 'I don't know if I'd want someone that scary as my brother. Imagine if you fought, he'd always win.'

'He wouldn't fight with you,' said Severus, leaning forward eagerly and almost toppling off the wall.

Lily's face fell. 'Tuney does,' she said softly, turning slightly away from him to pick at a scab on her knee.

'Tuney's stupid, just ignore her. No one proper would fight with you.' He leaned close, trying to get her to look at him. 'Come on Lily, stop worrying about her, she's a Muggle. You'll have to leave her behind you know, when you go to Hogwarts.'

She looked at him, her green eyes swimming with tears. 'I don't want to leave her behind, Sev. I want us to be friends, like we used to be.'

Her tears caused a pain in his chest. He felt as though he couldn't breathe properly all the time she was so sad. 'Don't cry, I'm your friend. I'll always be your friend, for ever.'

She snuffled and gave him a sidelong look through her lashes. 'Thanks Sev,' she said, wiping her face. 'I'm just being silly. Mam says it'll all blow over.' She gave a smile, then noticed the lengthening shadows and jumped down from the wall. 'I've got to go, they'll be cross if I'm late again.'

He cast a resentful look at the sky for spoiling his plans. 'Shall we meet here tomorrow?'

'I can't, Sev, we're going to get my school things, remember? It's going to be so amazing!'

He didn't share her smile, and looked away, his feet scuffing the brickwork. 'Thought that was next week,' he said sulkily.

'Oh come on, Sev, don't be such an old grump. Won't you have to go and get your own things soon, anyway?' She reached out and patted his leg.

'Mam keeps saying she'll take me then changing her mind,' said Severus somewhat reluctantly, not meeting her eye. 'Says she has a headache, or Dad's in too bad a mood to chance it, or the weather's not looking right… whatever. If she doesn't take me soon I'm going to have to start school without any things.'

Lily frowned at him, baffled. 'But your Mam's a witch?'

'Maybe she likes pretending to be a Muggle.' He started pulling a loose thread on his sleeve, avoiding Lily's now anxious gaze.

She took a deep breath, and then said, 'Why don't you come with us?'

He looked around so suddenly he almost fell off the wall. 'Really? Can I?'

She was a little taken aback by the greedy fervour in his eyes. 'Yes, I think so. I'll have to check with Mam and Dad.'

A shadow crossed his face. 'Listen, if they don't want me hanging round, I could just go off on my own once we get there, but I don't know how to get to this place without a grown-up to take me.'

Lily reached out and hugged him awkwardly. 'Don't be silly, Sev, of course you can hang round with us. Now I really do have to go, they might not say yes if they're cross with me.'

They parted their ways, Severus heading for the old mill workers' terraces, Lily for the bigger houses on the other side of the river. At the end of the alley, Lily turned to look back at her friend. Severus was walking quickly, head down, his arms jerky and awkward at his sides, feet occasionally lashing out to kick at a stone. She'd known him for a year, but only now did she wonder if she'd been asking him the right questions all along.

Very early the following morning Lily called for Severus. It was the first time she'd been right up to his house. The door was opened by a thin, unsmiling woman, dressed in an old fashioned plain brown dress and apron. On sight of Lily her face made no change from its dour expression. Lily however smiled brightly. 'Oh hello, Mrs Snape, is Severus at home? He's coming to London with us today, and we're leaving earlier than planned, so I thought I'd better come and get him.'

'Oh aye,' she said, standing aside. 'Wait int kitchen and don't make a noise.'

Feeling suddenly rather nervous, Lily entered the hall. Mrs Snape disappeared up the narrow staircase, and Lily found her way to the kitchen. The house was far smaller than her own, and very bare. It gave her a sad, creepy feeling. After a minute or two, Mrs Snape reappeared, shutting the kitchen door. 'He's coming,' she said tersely, and busied herself making tea. Lily stood in the corner, feeling horrible. She wasn't used to adults being so unfriendly.

'Severus tells me you're a witch?' asked Lily, after the she could bear the awkward silence no longer.

'Severus ought to learn to keep his mouth shut,' said Mrs Snape shortly, catching the kettle off the stove before it whistled.

'Oh no, it's all right, I'm a witch too! He wouldn't tell just anyone, I mean. It must be wonderful, being able to do magic.'

Mrs Snape gave a strange laugh. 'Magic is as magic does,' she said darkly, buttering two pieces of bread. Lily watched as she laboriously hacked some pieces of cheese off a block and slapped them in between the two slices. She cut the across thing wonkily to make an untidy sandwich, which she forced into a shabby paper bag. Lily wondered why she didn't use magic, but didn't dare ask.

Footsteps sounded outside the door, and to her relief Severus appeared. He was dressed untidily, his hair unbrushed, his face still bearing traces of yesterday's grime. Lily expected Mrs Snape to tell him off, but she gave no sign of having noticed. He had a hollow-eyed, anxious look, and even his smile had a nervous edge. Mrs Snape held the sandwich out to him gracelessly, and led them into the next room. She climbed onto the arm of the sofa to reach down a thick book from the top shelf. She glanced at the stairs before removing a wedge of notes from inside the cover.

Climbing down, she handed the money to her son. 'Lose that and you'll wish you were never born,' she whispered, glancing again at the stairs. Severus forced it into an inside pocket of his smock, and gave his mother one of his crooked smiles. 'Behave yourself,' she said, touching his shoulder just for a moment. A sound from upstairs made both the Snapes jump and look fearfully ceilingwards. 'Go on, hurry up,' said Mrs Snape, shooing the children towards the door. Before Lily could even say goodbye, they were on the doorstep and Mrs Snape was shutting the door.

Severus looked as uncomfortable as Lily felt. She felt as though she'd seen something she shouldn't, like she'd caught him on the toilet. He started off down the path, and she hurried after him. Halfway along the road she caught him up and grabbed his hand. 'Come on, Sev,' she said kindly. 'We're going to go and be wizards, remember?'

He smiled properly, and they began to run, hand in hand, towards Lily's house, and Diagon Alley, and a whole different world.