River has the whole of time and space at her fingertips. She sees distant stars, journeys through history, meets monarchs and artists and scientists and scholars.
It's almost like travelling with the Doctor, except this time, none of it's real.
The data core of the Library is peaceful, now. CAL is happier, no longer responsible for thousands of lives, and instead just Charlotte again, able to get on with the business of being a little girl - the little girl she's been for centuries. She has playmates and a dad and the kindness of Dr. Moon.
Dr. Moon is no longer so concerned with telling the Library's inhabitants to forget, but instead content to quietly exist in the background, a steady presence, there to help. He's honest with River, when she talks to him.
"You don't need my help forgetting any more -- the belief you carry is unsustainable. You cannot live in this world, here, if you believe none of it is real."
"But it isn't."
"Well, Professor Song, that rather depends on your perspective, doesn't it? True, the fact that you and I appear to have physical bodies in this place is an illusion, but your consciousness and my own are very much real, and so are our experiences."
"Your consciousness? You're just a computer program."
"Ah, but I'm a very old computer program, one who has had to develop and adapt to deal with the needs of the biggest computer in history. I think it's fair to say I've picked up a trick or two along the way." He smiles, sadly. "I envy you, in a way. Your physical self still exists, stored away as an energy signature."
River's stomach drops with a sudden and painful kind of hope. "It does? Then you can take me back, just like with the others, you wouldn't need that kind of massive energy surge for just one person."
He shook his head. "And the shadows would be upon you within seconds. It's too dangerous, I won't allow it."
River turns this over in her head. Her perennial instinct to fight back against all limitations has been at least a little tempered by age and a kind of hard-won wisdom, and she sees the sense in Dr. Moon's words. She can do many things and has defeated so many enemies, but she can't survive a forest of Vashta Nerada alone and with no resources.
"I suppose I'll just have to wait, then," she realises.
"For the Doctor. He always comes when I need him, eventually."
Dr. Moon looks unconvinced, but he leaves her to her thoughts.
None of this is real. It's the first thing she tells herself every morning, before she opens her eyes.
Then she goes about her day, existing as best she can while she waits for her next move to present itself. The trouble, Dr. Moon is right -- her own mind betrays her. She forgets that she's inside a computer program when she looks up at the boundless blue sky, or shares a joke with Anita. It's only at the end of the day when she suddenly recalls what she's forgotten, and has to focus on her breathing as the horror of her situation hits her all over again.
Some days, she doesn't remember at all.
River mounts an expedition to Deserts of Sothun. The archaeological discoveries there had been one of the stories that had first inspired her when she learned about it at school. Now, she gets to live it.
The temple in the middle of the desert is beautiful and ancient, and slowly she works together with Miss Evangelista and Other Dave to illuminate the place, recording everything as she goes. She knew, once, exactly how this goes, but now she's forgotten, and grins at Dave in excitement as he heads up the stairs.
Miss Evangelista turns to her with a worried expression on her face, and for a moment something chills River all the way down to her bones, though she doesn't understand why. It's an unexplainable relief when she is simply presented with a broken holocam.
It's moments like this that she lives for, she knows. The thrill of discovery, of learning things her peers don't already know. This one's a really big coup, and the professors at her university will be sour that they didn't believe her, that they wouldn't finance her on this 'fool's errand'. She's won again, she thinks, and maybe this time they'll give her tenure.
She doesn't remember that she really visited the temple with the Doctor, thousands of years previously when it had still be humming with life, and how she'd heard all the stories behind the statues. She doesn't remember that she already has tenure, that after her wild life of breaking every law in time and space, of cons and robberies and murders and heroism and saving the universe, she'd returned to the academic life and regaled her students with stories they never believed. She doesn't remember how the university only tolerated her because since they made her Professor of Archaeology, applications to the department had shot through the roof, and they'd started pulling in students from across half of the galaxy.
She doesn't remember that she's dead, and that all of this - the temple, the adventures, the home she's made with the others - is little more than a dream.
She's back home in that big old house where she lives with her friends and the children - if she thought about it too much, River probably couldn't say whose children they were, so she doesn't think about it. Dr. Moon visits regularly.
One day, River senses trouble. He's talking urgently with Charlotte, low voices emanating from the next room, and they both fall swiftly silent when River goes to see what's wrong. She heard enough from the corridor, though.
"What do you mean, there's someone in the library?" she asks.
"No," Charlotte snaps, fear making her petulant, "you're not allowed!"
"Charlotte," Dr. Moon says quietly, "maybe River can help us."
"Of course," says River.
"Do you remember the Library?" he asks.
"What library--" she starts. Then she stops. Then she remembers. "Yes."
She presses her lips together, hard, and she doesn't cry, because she never cries, but there's a flood of feeling all the same. Meeting that past Doctor, the one who didn't know her yet, and the pain that raced through her body as she died. She takes a few quick, short breaths, and then she's back to the moment, ready for anything.
"Someone's in my library," Charlotte says -- CAL, River remembers. "They mustn't be there, they're in terrible danger."
"I don't understand," says Dr. Moon. "Lux sealed the Library for good, no one can get in or out any more, even if they did decide to ignore all the warnings. But somehow, someone just appeared inside."
"Have you got visual?" River asks, and Charlotte presses a button on the television in the corner.
She doesn't really need the image to confirm what she already knows -- the Doctor is here. Her Doctor, because he always comes when she needs him. That beautiful blue box that flickers into view is just joyful confirmation.
"I'm going back," she realises, as the world around her starts to go out of focus. And there's no time, she realises, because the Doctor's a bloody Time Lord and still can't figure this stuff out - no room for goodbyes. She opens her mouth to say something to Charlotte and Dr. Moon, at least, but it's too late. The world goes white.
She comes to in the computer core of the Library. If she'd thought about it, she might have expected to still be in her space suit, wires clutched in her hands, but instead she's dressed simply in black, and there's no sign of the contraption that she'd died to activate. She wonders how much time has passed.
"River! Come on, run!"
She looks up. The TARDIS is across the room, its doors wide open, and the Doctor is holding out his hand. River starts laughing; this, she remembers. She runs towards him, and takes his hand.
The Doctor pulls her into the TARDIS and then slams the doors behind them. He pulls her into the light and turns her in a circle, muttering a little frantically to himself.
"All right," he says, slowing down. "One shadow. One shadow. Ha! I am a genius!" Then he sweeps her up in a hug, and River clings back fiercely. He continues to be a madman, and in a moment she's going to make him tell her exactly what he did, but oh, she's missed him, and this, and everything.
They disentangle, and the Doctor is unabashed as he wipes his sleeve across his face. River smiles, and squeezes his arm.
"New you," she says, taking everything in. The TARDIS has redesigned herself again, all sleek silver and coloured lights. As for the Doctor, well, she doesn't think she's even seen a photograph of this version before. Her eyes roam over him, noting the long hair, dark against his light brown skin, and her mouth quirks as she looks at the tight trousers he's sporting along with the crisp shirt and artfully cut jacket.
"Oh, sweetie, were you feeling your age a little?" she asks.
"Do you like it?"
"Mmm, very much," she says approvingly. "I look forward to giving it a test drive later."
The Doctor ducks his head, laughing.
"Before all that, though. Explanation, please."
"Right then." He claps his hands together and bounds over to the TARDIS console, which apparently now primarily operates through twisting mirrors to refract light in different patterns. River's looking forward to learning how it works. She races up after him, delighting in the feel of being grounded in her body again, the vibrations of the TARDIS soothing under her feet.
"Right from the start, I promised myself I'd come back and save you one day - save you properly, I mean, not just upload you to a hard drive. Took me a while to realise just how much you'd hate me for that, but I didn't know, not at the time. Then, later, I couldn't do anything to change what had already happened. But I could come back for you. Just a case of bypassing the Library's security protocols so I could set down directly into the data core, luring the Vashta Nerada away for a few minutes, connecting the TARDIS to the computer network remotely to give it enough power to download your energy signature and, well. Here you are."
"Here I am." River kisses his cheek. "Thank you."
He beams at her. "You're welcome."
"So, new regeneration. Where are we this time?"
That question has always been accompanied by the familiar flicking through of pages, and it's only now River realises that she doesn't have her diary any more. She knows every word and every story off by heart, but it still leaves her feeling unbalanced.
"That's the thing," the Doctor says. "I think we've gone full circle, now. The last time I saw you was when we went to see the singing towers."
"And the last time I saw you was the first time you saw me. Which means our timelines have synced up." River's eyes widen. "No more secrets."
"No more spoilers," the Doctor agrees.
"Well, that takes all the fun out of it," River says. She doesn't have to say what this really means to her, because he already knows.
"Fun?" The Doctor looks indignant. "River Song, I'll show you fun." He locks eyes with her as he adjusts the controls, and she laughs as the TARDIS rocks a little.
"You still can't fly her properly!" she protests.
"I thought you said you wanted fun!"
And she does; she really, really does. So she reaches out and takes the Doctor's hand in hers. He's still smiling, and they're flying, and it's just like the start all over again.