He was lonely. He always had been, he supposed – his friends were just brief respite. Patches of light in his otherwise bleak life. It had been so, so long since he had lost Amy and Rory, and he hadn't wanted to find anyone else. River had kept telling him to, of course; she couldn't bear the thought of him alone permanently. But it had been so long since he'd last seen her – at Darillium - that he was positive he'd lost her too. Darillium was the last time for her before the Library, but he'd tried to cling on to the hope that he would see her again. He didn't think it would happen, now, though. Nothing ever lasted.

He sat in his swing beneath the console, just remembering. Remembering River, and the Pandorica and the Byzantium and Utah and Berlin and Calderon Beta and, oh, remembering Darillium.

She was out of Stormcage by then. Just days previously, she had been asking his advice on whether or not to take up a job offer she'd received – leading an expedition to a planet of books that had been silent for a hundred years. And though it almost killed him to say it, he'd told her to go for it. I expect I'll be seeing you there, she'd told him with a grin, and he'd forced a smile onto his face and answered with 'Spoilers'.

He knew it was time then.

He'd worn the same suit as for Calderon Beta, and he'd finally coaxed her into that dress. They'd talked and kissed and made love under the stars, and as they lay listening to the melodies of the towers, he couldn't hold in his emotions any longer. He'd cried, and River had too, though she didn't know why. The night had been so perfect, and yet it had been the saddest night of his life.

'Doctor!'

His reverie was broken by the sound of River's voice. Clearly the TARDIS had decided to pick up her call without giving him any choice in the matter. He was elated for a moment, but then remembered the last time she'd phoned. It had been for the wrong him – the River in that phone call hadn't even done Jim the Fish yet, and the Doctor had had to fight to conceal the disappointment in his voice as he told her to try again later.

'Hello? Doctor, are you even there?'

He placed a hand on the console to steady himself, and he felt the TARDIS hum gently. He knew his ship by now, and she knew River even better. He knew the TARDIS was telling him it was right, it was fine. It was this version of himself that River was looking for.

Gingerly, he picked up the phone.

'Yes. I – I'm here.'

'Oh, sweetie, thank goodness. You have to come here now – hang on, diaries. Have we done Darillium yet?'

'Three times, but the last one – the one where you wore the green dress – that was nearly a year ago.'

'And have you seen me at all since then?'

His voice caught in his throat, and he choked back a sob. 'Spoilers'.

She laughed – oh, how he missed that laugh! – but when she spoke, her tone was serious. 'Doctor, have you been alone for all that time? Don't answer – I know you have. Oh, you can't do it, you know. You think you're completely independent; you think you only take people with you for their benefit, not yours. But I know you, and I love you, and Doctor, you need someone.'

'River, I-'

'I didn't mean to phone just to tell you that, anyway. I've got a surprise for you. Earth, fifty-second century, N258.6⁰SW42.89⁰. Don't worry, the TARDIS knows exactly where.'

'River, please. What's going on?'

She swallowed. 'I – I can't tell you, my love, I'm sorry. Spoilers. But I'll say this – it wasn't the end.'

'River – River – what?'

'If you have to ask, you'll never know. See you soon, sweetie!'

The connection cut off, and he leaned against the console, confused. She couldn't be calling him. Not this River. Not his River. His River was dead. If she'd been to Darillium, then there was nothing else left for her. End of the line. There was, really, only one very simple explanation – it was a mistake. But he'd turn up anyway, if only to see her once more. Then he'd put her straight. Tell her she'd got the wrong version of him, and leave without another word. So much for thinking the TARDIS knew where they both were temporally – his ship had got it wrong.

As if in response to his last thought, the TARDIS hummed angrily, and set off, following the coordinates. The Doctor sighed and stroked the console, feeling the ebb and flow of the matrix beneath his fingers.

He was going to see River one last time.

When they landed, he closed his eyes for a moment before checking the scanner. Earth. 5180. Hospital.

Hospital? He thought with a twinge of panic. River had been secretive, even more so than usual … could she be in trouble? His breath quickened as images of her ill, injured, dying, flooded his mind. He raced to the door and flung it open, suddenly worried for her.

Instead he entered a room flooded with soft, golden light. He searched the room quickly, and found her asleep or unconscious in a bed at the other end of the room. He almost sprinted to her bedside, ignoring the nurse that stood beside her.

'Doctor.' It was the nurse who had spoken, and the Doctor turned around, fearful.

'Will she be all right?' His throat was dry.

'She'll be absolutely fine. She contacted you around seven hours ago, and she's been asleep since then. She should wake in a few minutes, if you want to stay?'

He nodded, and the nurse left the room. He turned back to River, and watched her quietly for a moment. She was so beautiful. How had he forgotten? And even if this was the wrong her, or the wrong him, or indeed the last time he should meet her, he no longer cared. He had memories, and memories were eternal.

He ran his hand through the hair that fanned out over the pillow, and felt her stir beneath his fingers. She opened her eyes, and smiled up at him.

'Hello, sweetie.'

'Hello.'

'Did you get my call?'

'Yes. About ten minutes ago.'

'Do you want to see her?

'See her? See … who?'

'Doctor! Stop it. You can't lie to me. See our daughter, of course.'

'Our daughter?' For the first time, he looked around him, properly taking in his surroundings. Just ten feet to River's left was his cradle, with its Gallifreyan inscriptions and battered hanging stars. The same cradle River had slept in so briefly as an infant. The same cradle his baby was sleeping in now.

He moved over to the cot and gazed down on his baby daughter. She was perfect, with her pink cheeks and her downy head and her hands, tiny little starfish hands that had wrapped around his finger instinctively the second he'd put it into the cradle. He blinked back tears and turned back to River, who was watching him carefully, her expression unreadable.

'What's her name?' he said, his voice thick.

'Amelia. I would have asked you, but I thought you'd like it. It fits her, don't you think?'

'It's perfect,' he said, 'Brilliant, wonderful, fantastic, amazing … and do you think she'll like the bowtie?'

She rolled her eyes. 'Given who her mother and grandmother are, I think disagreement on this is a family trait.'

'River, when did we – I mean, when was Amelia, you know-'

'When was she conceived? At my house. After the Library.'

Both of his hearts nearly stopped. 'After the Library? But River, that's not possible. The Library – I was so young, and I didn't know you, and you – you –'

'I died. Yes. I know. I was there, sweetie.'

'Then how can you be here?'

'I-'

'Here, real, post-Library, talking to me, with a baby you're telling me is our daughter,'

'Yes, I - you-'

'although it simply isn't possible for her to exist!' His voice rose in anger and he turned and paced the room, his mind racing. Why did she have to be so damn River all the time? Couldn't she take a day off from teasing and riddles and mystery and 'spoilers', and stop being so bloody impossible?

'Doctor, if you'll just listen I am trying to tell you! I died, and you saved me! I was in the virtual reality with Charlotte and my team. I was there for years, or months, or no time at all – I don't know. I don't know how time passed in that place. But one day, I was there one minute and the next I was in the TARDIS again. With you. I don't know how you did it – I don't remember much of that part of it. But you took me back to my house exactly six weeks after I'd last left it. You were aiming for the same day as I'd set off, but you tripped over a wire and overshot it. Anyway, you landed at my house, and then a fortnight later, I found out I was pregnant.'

The Doctor stumbled to a chair and sat down heavily, struggling to make sense of it all. 'You're telling me I saved you? But I didn't, I couldn't, I – oh.'

'Doctor?'

'When I was young, in the Library, I saved you. To the computer, with the neural relay in the screwdriver. So I can do it again! I can go back and download you, I can get your consciousness out of the computer and project you through the TARDIS, and –'

'No, you can't. Vashta Nerada, remember? They've got the planet for the rest of time. You can't ever return.'

'Then I'll find another way. River, I have to save you, or this will never happen! You've already created a massive paradox just letting me know! I know you, River Song, but what in the name of goodness possessed you to do this? '

She stared at him for a moment, her face set. 'You. You told me what to tell you the night you saved me. Doctor, you'll think of a way. You will. I know you too. It just had to be this way. You'd given up, hadn't you, sweetie? You needed something to show you there was hope – that there was a way out. That the Library wasn't the end. These are our last spoilers, you know. We're in sync after this – you and me, travelling forward together.'

He buried his face in his hands as his brain whirred, and tried to expel the doubts from his mind. It can be done, he thought. If River's here, then it has to be done. And if I can't go back to the Library, I'll have to find another way. I've got a copy of her neural relay, so I could – no, too risky. But if I reroute the sample of her DNA through the Artron energy in the matrix – that might even work.

River felt a lump rise in her throat, and averted her eyes from him. I'll be erased. He can't do it. He won't be able to do it by himself, she thought. 'Sometimes I wish he'd just let me help him. He can't do it alone. She blinked, cleared her throat and spoke.

'Sweetie?'

The Doctor looked up to find River watching him tenderly, tears in her eyes. 'Doctor, if you can't do it then I – I'll understand. I mean, I've seen you once more, and I've had all of this. If I have to – go back, I'll still love you. Forever. Like I said, you and me; time and space. It was a good run, wasn't it, my love? All those hundreds of years – I'll still have those even if we have to erase these last few months. Memories are eternal.'

She was crying now, and he hadn't thought it possible to feel so weary. This was River. She wasn't just the woman who walked out of prison like it was a hotel, or who broke time to teach him a lesson. She was River Song – the woman who gave first her freedom and then her life just so he could go on, and was willing to do it again. Willing to undo the continued existence of her and her daughter, just for him. And the thought broke his hearts.

'No, River, please don't think like that. Memories are eternal, but they're not enough. I need you, and I'm going to get you back. I can do it. I've got an idea, and I think it'll work. Five minutes. I promise.'

She nodded and smiled, but already her eyes were closing. He leaned over and kissed her softly, before walking away. As he reached the TARDIS doors, he heard the nurse re-enter the room. He turned and acknowledged her and she inclined her head, lifting a whimpering Amelia from her cradle. His breath caught in his throat. He didn't just have to try for River, he had to try for her. Little Amelia, less than a day old. He had to try to save River for her.

He could do it. He knew he could.

He'd do it for all of them.

In the TARDIS, he felt more hopeful. He had a plan – more than that, he had a realistic plan – and he had a way of carrying it out. Artron energy. Invisible to most species, but he could see it. Tiny particles of gold clustered around everyone and everything to ever travel in time. All of his companions were golden in more ways than one, but River was special. She was the child of the TARDIS, conceived in the vortex, and she shone like living gold. If he connected a sample of her DNA to the matrix, the TARDIS could bring her back using simple quantum entanglement – that is, use the Artron energy in the matrix to find the only living replication of that DNA and pull River back through the vortex.

He went to work, flicking levers and switches and searching through masses of data on the scanner. He knew the TARDIS knew what to do, and he watched in awe as the central column glowed brighter and brighter until it was almost white and pulsating with energy. He pulled up the analysis of River's DNA on the scanner and fingers crossed, transferred it to his ship's heart.

The Doctor clung on to the console as they spun through the vortex, trying not to listen to the sounds his ship was making. She was hurting – she wanted River back just as much as he did, but the necessary process was almost too much for her. Curls of energy began to spread around the room, weaving themselves together; a web of time. He'd seen her do this once before and he followed her every step with his eyes.

'Oh, look at you. Look at you go!'

There was a blinding flash and the TARDIS jerked violently, throwing him onto the floor. When he looked up, all the energy had receded and River was there. He scrambled to his feet and moved to embrace her, smiling. But it only took him milliseconds to realise something was wrong and he lunged forward, catching her as she collapsed and lowering her unconscious form to the floor.

'River, River, please wake up, please. This shouldn't have happened, you shouldn't have collapsed, it's all gone terribly wrong – scan her, please!' He begged the TARDIS, biting his lip.

There was a familiar whirr and he reached up, pulling the scanner down to read its result. Temporary lethargy caused by unprotected exposure to time energy. Recovery time approx. 22 minutes.

He sighed with relief. Of course. She hadn't had anything to protect her from the vortex – not even the few microns of protection her vortex manipulator usually gave her. And though she'd only been exposed to it for a millisecond, perhaps less, she wasn't completely Time Lord – it was still a danger to her. But she was back. She was safe, and in twenty two – no, twenty one minutes, she'd be absolutely fine.

Still, for the Doctor it felt like he'd waited an age. He pressed his ear to her chest and listened for her heartbeats, just to make sure. Took her pulse from several different points, just to make sure. Got the TARDIS to scan her again and again, just to make sure. Then finally, she moved and he loosened his protective hold on her. Her eyelids fluttered open and she focused on him.

'Doctor?'

'River! I was so worried, I thought I'd lost you again. Are you … are you feeling all right? You did just get pulled through the vortex. Unprotected. I need to stop doing that with people. It's …' His voice trailed off; River was shaking like a leaf in his arms and muttering under her breath, clearly terrified.

'No. It's not real. It isn't. I'm dreaming, and I'll be back in the grounds with Dave and Anita the second I open my eyes. But this is a cruel dream. I'm dreaming of the one place and the one man I can never see again, it's not real, it's not – it's not – it's not –'

She was squeezing her eyes shut and her fists were clenched. The Doctor shook her gently. 'River, it's real. I saved you from that place, and we're together again. Look. Open your eyes.'

Her eyes were still shut as she spoke again. 'How?'

'Artron energy. I transferred the records of your DNA into the heart of the TARDIS and kind of pulled you back through space. Like I had a big magnet with – with River-DNA on it. Anyway, it found the replication of that DNA – you – and pulled you here. But I forgot about the you-travelling-through-the-vortex-unprotected thing and you've been unconscious for nearly half an hour. Oh, River, this is brilliant! '

River dared to look around her then, and tears filled her eyes. 'You did it, my love. You saved me. And I thought I'd never see you again …'

She buried her face in his shirt, and he held her there for a moment before helping her to her feet.

She smiled happily at the Doctor as he danced around the console, pushing buttons and keys and levers like the happiest man in the universe. He set the coordinates for her 52nd-century home on Earth, not an hour after she'd last left it.

Skipping over to her and winding his arm around her waist, he waltzed her around the control room and only tripped over once. His foot caught in a clump of wires poking out from beneath the console and he fell, ripping the wire out and causing the TARDIS to change her destination slightly.

'Whoops. You might be a couple of weeks late now.'

'Oh, it doesn't matter, sweetie. Better late than never, and until now I was never going home at all!'

The TARDIS landed with the familiar noise, and the Doctor grinned.

'Back home, River Song.'

He held tightly to River as they entered her house – she still wasn't perfectly steady on her feet and he didn't feel like he wanted to let go of her again, especially not tonight. If River had been away for her house for six weeks by Earth's time, and Darillium had been two weeks before this for her, and by his timeline it had been around a year between Darillium and the birth of Amelia ... well, he wasn't stupid. He knew what tonight was.

Much later, he remembered something.

'River?'

'Yes, sweetie?'

'We've still got spoilers, you know. Or, rather, I have one for you. Quite soon, you'll meet a me who hasn't saved you yet. I mean, he's not – I'm not much younger than this me – it's me from a few hours ago, basically. It won't be the next time you meet me, you've a while to go yet before you do. But when you do meet him, you'll know, and you have to tell him that I saved you. Will save you. Have to save you. Otherwise I'll just ... leave, and our timelines will unravel again. Do you understand me, River? Only it's very important that you do this. River?'

She looked up at him from the bed and giggled. 'Of course, Doctor, but how do you expect me to take you seriously with that on your head? Of course I'll remember, sweetie, but take it off, you look like an idiot.'

He stuck his tongue out at her. 'Hey. Fezzes are cool. And I did just save your life, so ... maybe tonight I can keep it. Please?'

She laughed again. 'Just this once. And – thank you, Doctor. Thank you for everything.'

As he lay down beside her, his hearts leapt with joy.

'River Song – it was my pleasure.'

He left in the morning, after promising her he'd come back to see her as soon as he could. As he skipped down the path, she waved from an upstairs window – he'd insisted she rest for the day – and he blew her a kiss, before snapping his fingers and disappearing into the TARDIS. He didn't even have to play with any controls – the ship took off almost as soon as he was through the door, and somehow he knew he wouldn't be late this time.

As soon as he'd landed, he bounded through the doors and landed with a jump in front of River. She was just waking, so he knew he couldn't have been gone long. As she pushed herself up her pillows he turned to his hours-old daughter and picked her up, rocking her gently. She gurgled happily and stretched her arms up to his bowtie, and he bent to kiss her forehead, whispering 'Hello, sweetie' in her ear.

'I did it, River,' he said, settling himself and Amelia on the edge of her bed. 'I saved you, for her. Amelia Song.'

Some days are special. Some days are so, so blessed. Now and then, every once in a very long while, every day in a million days, when the wind stands fair and the Doctor comes to call ... everybody lives.