A/N: I've been wanting to write a crossover involving River Song and River Tam for quite a while, and after having River Song's identity confirmed in A Good Man Goes to War, with the added bonus that some terrible government-type force wants to turn her into a weapon, well...too shiny to resist. I am unfortunately taking calculus this summer, so depending on how much work that turns out to be, I may or may not be able to promise regular updates.

Disclaimer: Moffat and Whedon own all. I own nothing.

2520

Somewhere, somewhen in the universe, River Song is twenty-five years old today. She's twenty-five years old here and now, too, in her own personal timeline, but she's not quite sure when it is outside of that or where, and she can't remember how she got here.

Well, first there was a Time Agent and then a Vortex Manipulator (of which she is now in possession, thank you very much, it's not difficult to pick a drunk man's pocket) and then the police might have been alerted and they weren't very nice and there's always the risk someone else is coming after her and her DNA, too, so she ran without thinking and may have landed a little harder than she intended.

Ow. Her head echoes with pain like a bombed cathedral. Yes, definitely landed hard…but where? Some kind of docks from the crates and such piled around her, but what kind, sailboats or steamers or spaceships? She pulls herself to her feet and climbs atop a pile of crates. Oooh. Spaceships. Good.

"You need a ride."

River Song whirls, hand going for the knife she keeps at her hip since she lost her blaster in an unfortunate incident with some neo-Egyptian space pirates. When she sees what's behind her, she relaxes a little but not much.

A girl, a few years younger than she is, maybe more. Not more than twenty, could be fifteen. Long brown hair, skinny, in a little dress and no shoes. Not a threat, half of River Song's mind thinks, but then she remembers that she's only a curly-haired girl in short pants herself. At least she has shoes. And her knife. But the girl is either naïve or keeping a secret because she's got her head cocked and is staring at River with the innocence of a child and the deep knowing of a seer.

"Who are you?" River Song demands, forcing a note of authority into her voice. The girl only laughs, not mockingly, but with genuine pleasure.

"River," the girl says.

"What?" River Song's hand finds the knife in her pocket and grips it hard. It's never good if they know your name; either you've been here later and don't know it or they're with the people who took you before and who will never ever take you again. Not alive, anyway.

"River," the girl says insistently. "I'm River Tam, and you need a ride, don't you?" This is what she says out loud, this is what River Song hears. What's tumbling through her mind instead is something more akin to Riverriver, like me, like you, you're a song and i'm a dance and you're a weapon too, aren't you, born in shining metal halls like me were there knives river like the one in your pocket in my pocket too? Don't leave home without it, never know who will want to play hide and seek on the way, Captain asks why we can't ever flow smooth, we rivers like to wind a song a dance around before we come in from the cold for the kill.

But she's twenty now, and well enough to be pilot as well as junior doctor to Simon 'case he's hurt or stranded or worried, well enough for Jayne to have started thinking things she'd rather not have in her head but not well enough to keep them out.

"Depends on where."

"Anywhere that's not here, or the place you're running from." She sees the other River's fingers tighten on the hilt of the blade in her pocket and smiles. "Good to have a knife, but you don't need it now."

"I don't know that I won't, seeing as you seem to know all my secrets, and in my experience, little girl, that rarely bodes well."

"Little girl's not a threat."

"That's what they want you to think, but I know better."

"You're a little girl, too. Little girl lost, taken away."

"See, how do you know that?"

"I know you're running because I'm running, too." If she weren't psychic, that would have been a risk, but this River is even more lost than she; doesn't even know what planet she's on or when, let alone who's wanted. Thinks she's wanted. Anyway, won't tell. "You're right. I'm a threat. Not to you. Like you."

"What do you mean?"

"You're a weapon, too." Blithely stated.

River Song is alarmed. River Tam has begun to dance a bit, executing a graceful spin before pulling herself together.

"How do you know that?"

"Told you," the younger River says, and turns to leave. "You need a ride. Come on, if you want one knows how to run fast."

Still fingering the knife in her pocket, River Song follows.

…

Captain Mal Reynolds is annoyed, and this is not ameliorated when he sees River leading someone who is probably a passenger and definitely some kind of trouble up the ramp and into the cargo bay.

"Who's that?" he yells, running—not running, moving at a dignified, captainly, but rather brisk pace is all—down the stairs.

"Passenger," River calls offhandedly, continuing onboard.

"This dump runs fast?" the other girl says.

River grins. "Course it does. I'm the pilot."

"Who said anything about passengers? Because I didn't, Li'l Albatross, and as I recall I'm the captain of this boat. Which is not a dump," he adds, glaring at the intruder.

"Captain, this is River, she's running." River says nonsensically.

"I need to call your brother, get some new meds or a new pilot, Albatross?"

River rolls her eyes theatrically. "No," she says, and gestures toward the other girl. "Her name is River also. River Song."

"I never told you that," River Song says, eyes narrowed.

River giggles. "Can't run from my secret and neither can you," she says. "Part of us, got inside."

"I don't like this runnin' talk," Mal says, concerned. "Passengers runnin' from somethin' bring nothing but trouble, Albatross!" He calls the last bit out because River is walking away. "Albatross!"

"Good luck, Captain," she says over her shoulder. "I know you know that."

"Stay out of my head!"

"Inara said. Wasn't over the shock you knew a poem."

Laughter lingers after River disappears over the bridge. Mal heaves a deep sigh and turns to River #2, which boded well as all gorram hell.

"Can you pay?"

River reaches a hand inside her bag, feels around, grins. The Vortex Manipulator wasn't all she stole from that Time Agent. "Yes, I can."