River Tam knows how to listen. She's been listening all her life to the things that people aren't saying, the things others can't hear. It was a dull murmur before the Academy cut into her and turned up the volume, made it more like shouting. She hears the grumble of Jayne's thoughts; the gentle whisper of Inara's; the happy babble of Kaylee's. And underneath it all, the rumble of Serenity, keeping them all afloat in the Black. But lately, she thinks there's something else. At first she thought it was the stars singing to her, so she pressed her ear to the window, trying to make it out better.

"What're you doing, River?" Simon asks, alarmed, when she presses herself up to the glass of the viewscreen.

"Shhhh," River says, annoyed at him. "I'm trying to hear the words."

Simon looks confused. He often does.

"The words to what?"

"The star-song."

But after a while she realizes that she was wrong - it's not a song the stars are singing, but a song about the stars. The Music of the Spheres. The melody is ancient and sweet and sad and lonely. Occasionally there are other harmonies woven in with the main melody, some as strong and vital as a heartbeat, some as gentle as a bird's song. It's beautiful. River loves to hear it. It makes her feel less lonely.

She can hear it best at night, when there are no other distractions. On this night, she lies on her back on one of the metal walkways of Serenity, staring up at the metal ceiling and listening. She wonders idly if she could answer back to the music. Experimentally, she hums a few bars, mimicking as best her limited human vocal cords can. In the open space of the cargo hold, the sound resonates off the walls, sounding bigger than it really is. Bigger on the inside. River giggles.

She hums again, but nothing happens. River lies back on the walkway and listens again. There is a beat of silence and then suddenly the hold is filled with another sound, a grating, grinding, vroping sound. River sits straight up, peering with surprise down at the hold floor, where a large blue box has just materialized.

She scrambles to her feet and dashes down the stairs just in time to see a man step out. He is wearing a tweed suit with suspenders and clunky army boots. His hair sticks straight out and his ears are very large. He has on a wide grin that seems to spread all the way across his face.

"Was someone calling for me?" He asks.

A woman shoves him aside, brushing sandy brown curls off her shoulder.

"Honestly, Doctor, it's not all about you," she says.

The Doctor frowns playfully.

"It most certainly is," he peers into the shadow of the stairway, where River is watching him with large eyes. "Hello there. Were you calling me?"

River steps forward. She knows she doesn't have to be afraid of this man. She recognizes him instantly - he is the source of the music. Oh, the things in his head! It's as if the stars themselves are born within his mind. All of time and space whorls around in dizzying colours and shapes. River feels punch-drunk.

"Oy, get out of there," the Doctor says, but not unkindly. "Don't you know it's rude to go rummaging in people's heads without being invited?"

His mind shuts to her with a clang, and River starts. There's never been a mind she couldn't get into.

"She doesn't know the rules," River whispers, feeling chastised. "She's never been told."

The Doctor peers at her.

"Who are you then?" he asks.

"River Tam," she replies.

The Doctor grinned.

"Another River! Brilliant! River Tam, I'm the Doctor, and this," waving to the woman beside him, who stands with her arms crossed, not amused at being ignored, "Is Dr. River Song. Two Rivers in one place in time and space. The universe may implode!" He looks delighted by this idea.

Dr. Song rolls her eyes.

"He's always a little giddy after we save the world. Can we help you, love?"

"I heard your song," River admits. "It was so lovely and sad. A Lonely Angel. I wanted to find out who the song belonged to."

The Doctor blinks at her.

"You heard my song? Oh! You heard the TARDIS!" He whips out a long tube with a blue end that looks like one of Simon's instruments, and buzzes her with it. "Hm, looks like we've got a class A psychic here." He frowns at the readout. "You didn't start that way, though. You were born a class C. What did they do to you, girl?"

"They cut and tore and made her a doll on strings," River says, in a slightly sing-song voice. "Now she hears, when all she wants to do is listen."

"Who did?"

"The Academy. Two by two, hands of blue. Cut and poke and gouge till I see what they want me to seem," River shudders at the memory.

Dr. Song comes forward, lifting River's chin with a long tapered finger and examining her face.

"You're so young," she says.

"Not a child," River says defensively, moving her face away from Dr. Song's grasp. She's tired of everything thinking she needs to be coddled and taken care of.

"Not an adult, either," the Doctor says. "You're caught in between, aren't you, River Tam? Between child and adult, between life and death. Between land and stars." He looks thoughtful for a moment, then changes gears. "Tell me about this Academy of yours."

Dr. Song rolls her eyes.

"Don't pay any attention to him, love. He has no manners at all. Not even any concept of manners. We can talk about creating psychics over tea. This young lady seems to be in need of some."

The Doctor blinks.

"Oh. Yes. Well, if you like."

He steps aside with a flourish.

"Come in."

River steps past him, into his blue box. The song is louder now, but not deafening. More like a soothing white noise in her head. River closes her eyes and marvels. The box is singing to her.

"You're beautiful," she whispers, putting a hand on the door and feeling the wood beneath her fingers. She opens her eyes and stares at the vast, cavernous room in front of her. "The inside is bigger than the outside. The dimensional transcendents of that are all wrong. Reality impossibility."

"Isn't it just," says the Doctor behind her, looking pleased. "Oh look, tea!" He points, and River follows his finger. At one end of the room, around the other side from the raised platform where a large blue control centre stands (that River is itching to get her fingers on), there is a blanket spread on the ground, with an old fashioned wicker picnic basket beside it. Dr. Song is already there, unpacking things from the basket.

"The TARDIS likes you," she says to River. "It's probably because you were admiring her. She's a vain old thing."

"She's lovely," River defends her new friend. "She's saying hello to Serenity."

"Is that the name of your ship?" asks Dr. Song. "That's pretty. Serenity."

"Name is ironic," River says. "Named for a battle. Serenity not serene. Not finding peace; looking for peace."

"Ah," says the Doctor. "Aren't we all?" He sits down cross-legged on the blanket, and looks up expectantly at Dr. Song. She obligingly hands him a delicate china cup, with affectionate exasperation.

"And don't eat all the jammy dodgers this time," she instructs him.

He gives her an innocent face, and sneaks a cookie when her back is turned.

River sits down, and spreads her skirts demurely over her bare legs. She sips the tea she has been given, blinking in surprise at its mild taste.

"I put honey in it," Dr. Song says. "I hope that's ok."

"Don't know," says River. "Never had it in my tea before. It's sweet. Sweeter than Kaylee's strawberries."

"Never had honey before!" the Doctor exclaims. "Blimey. This is a grim time in history. Next you'll be telling me you don't have biscuits." He settles himself comfortably on the picnic blanket, and looks at River with a penetrating gaze. River shifts uncomfortably. It's been a long time since she couldn't look into someone's head and see what they were thinking about her. "So, River Tam. Tell me about the Academy. Because you shouldn't know how to create psychics, not for another thousand years, and even then it's a disaster."

The memories rush upon River like the tide, as brutal and relentless.

"They took the pretty girl who loved to dance, and they taught her how to kill. Drove needles into her eyes and asked her to See." the china cup in River's hand rattles in its saucer as her hands shakes. Dr. Song takes the cup away, and replaces it with her own hand, dry and warm and steady.

"Let me get this straight," says the Doctor, sitting up. "There's a place out there creating psychics by cutting into children's brains?"

"Wanted to make weapons. Programmable people, dancing to their tune."

There is something hard that settles into the Doctor's features.

"I see," he says. He exchanges a look with Dr. Song. "And where exactly is this Academy?"

"Osirus," River says. She glances at them, her head tipped sideways. "What are you going to do?" Because there isn't any doubt in her mind that this impossible man in his impossible box, this Doctor, is going to do something.

"What I'm going to do, Miss Tam, is stop them from hurting anyone else. The human race is not meant to have anything higher than Class B psi abilities. Your minds weren't made for it. Any higher and they start to fracture." He looks pityingly at River. "Like yours."

"Is there anything we can do for her, Doctor?" asks Dr. Song.

"I can put up a barrier between your mind and the world, a sort of filter if you will," says the Doctor to River. "But I can't replace what was lost. Do you want me to do that?"

River considers.

"Will I stop being useful to Serenity?" she asks. "Will I stop being me?"

"It'll be a filter, not a block," says the Doctor. He reaches out his hands, placing them one on each temple. "May I?"

River nods and closes her eyes.

"If there's anywhere you don't want me to be, just imagine a door closing, and I won't be able to see it," the Doctor instructs.

His mind slips into hers, but it doesn't feel like an intrusion. She can feel him searching for the missing part, but while he does, she can feel bits of him slip through as well. He's so much more than he seems at first glance. She can see the sun and the turn of the universe and all of time and space, every star that ever was.

"Doctor," she breathes. "You're bigger on the inside."

The Doctor yanks his hands away.

"I told you not to go rummaging!" he says sharply. He sighs, shakes his head. "I've put a filter in your mind. You should be able to keep out the worst of it now."

"Thank you," says River. She looks at him, and then at Dr. Song, who has been watching with a fascinated expression on her face. "You're going to go after the Academy aren't you?"

"Don't have a choice," Dr. Song answers. "Can't have them doing to other people what they did to you."

"Want to come with us?" the Doctor asks.

River considers his offer for a few seconds, considers it very carefully. She has seen what he does, in his head. She has seen the kind of life she leads. She knows if she goes with him, she won't come back the same, if she comes back at all. And sometimes they don't. Sometimes they travel and travel with him, and end up so very far from where they started.

"Can't," she says regretfully. "Have to stay with Serenity. Have to help find peace."

The Doctor nods, understanding.

"But don't worry. We'll get to the bottom of this. I'll send you a post card, tell you how it turns out."

River is about to ask what a post card is, when a clanging sound interrupts her.

"That would be our signal to go," says Dr. Song, jumping up and racing to the control panel. "Doctor, the mauve alarm just went off in sector two." She smiles at River. "It was lovely to meet you, dear."

"Nice to meet a fellow River," said River politely.

The Doctor shows her to the door. He stands awkwardly in the doorframe, grinning at her.

"Take care of yourself, River Tam."

She nods solemnly.

"Take care of yourself, Doctor."

He grins.

"Don't I always?"

Simon finds her lying on her back on the grating above the cargo hold. She is tracing the ceiling with her eyes, and thinking about how much of the universe can fit inside one head.

"Where have you been?" Simon asks, rubbing the back of his neck sleepily. "It's almost the end of the sleep cycle and you weren't in your bed."

River glances down at the cargo hold, where a blue box stood only moments before.

"Been listening," she says. "To the song of the stars. Two Rivers in one box. But the universe stayed intact." She turns to Simon and smiles. "Everything's going to be alright now," she says. "Maximum velocity achieved."

She gets to her feet and wanders away, humming quietly to herself, leaving Simon to stare after her with a puzzled expression.