Amy Pond is twenty years old when she wakes in the middle of the night and sees a strange woman standing in her garden.

The woman is short, youngish, blonde. Trespassing. Amy squints into the dark, her nose pressed to the window. Her breath fogs the glass, and she frowns. “Truncheon,” she mutters, and in the bed Rory stirs.

“Mmm?” he says, still asleep, half his face mashed into a pillow. “Amy? Wha’s wrong?”

“Nothing,” she says, and stuffs her feet into an old pair of wellies. “Shut up. Go back to sleep.” She drops down to her knees and digs her costume truncheon and radio from the mess beneath the bed. Rory rolls over and makes a quiet, discontented sort of sound; Amy tucks the truncheon under one arm, reaching over to tug the body-warm blankets up to his chest. “Idiot,” she says, her voice soft.

Rory smiles in his sleep.

She creaks down the stairs and into the front hall. Her heavy winter coat hangs from a hook by the door; she pulls it on over her pyjamas and slips silently out into the cold. The pavement stones glitter with frost, slick beneath her heavy boots. She steps softly around the worst bits of ice as she walks through the vine-choked arbour.

The woman wears black trousers, a blue jacket, and a pair of sensible black shoes. Her hair catches the faint light from the kitchen window, and she stands stiff-kneed in Amy’s garden, staring at her shed.

Amy raises her truncheon and steps forward.

“Hello,” the woman says without turning. “Are you going to hit me with that?”

“Maybe,” Amy says. “Thought I’d wave it about a bit first.” She takes a wary step closer. “I’m a policewoman, you know. You should probably shove off before my backup arrives.”

“Probably,” the woman says. She frowns. “How old is this shed, would you say?”

Ah, Amy thinks. A nutter, then. There’s a sharpness to the woman’s eyes she wouldn’t expect in someone high or slightly less than sane, but it’s hard to be sure in the dark. Amy takes another step. “It’s been there for twelve years. Almost thirteen. Does it matter?”

“It might,” the woman says. She touches the wood with one pale, ungloved hand. “What was here before that?”

“A different shed. Something landed on it.”

At that the woman turns and meets Amy’s eyes. She looks terribly sane. “Something?

Amy doesn’t talk much about the Doctor anymore, not since the Atraxi and the day a man and his dog almost ended the world. Rory treats her silence like grief; in reality, it’s something more like stubbornness. She isn’t ever going to forget the Doctor, but she doesn’t expect to forgive him, either.

Something about the woman’s thin, weary face makes Amy think she’d understand.

Amy lowers the truncheon to her side. “Why are you here?”

“I’m looking for someone. I thought I might find him here.” She gives Amy a slight smile. “Don’t worry — I’m used to disappointment. I’ve been looking for a long time.”

Amy has never met anyone like the Doctor — has never even imagined that there could be anyone else like him. It’s an absurd idea, really, and yet–

“Are you from the future?”

The woman stares at her, eyes wide. “What? No.” Then her lips twitch in rueful amusement. “Well, yeah, actually. A bit. But then, I’m also sort of from the past.” She shrugs. “My timeline’s a mess. I lost track ages ago.”

Amy’s eyes narrow. “You're not an alien menace come to destroy the Earth, are you?”

The woman laughs. “Have some experience with those, do you?” She shoves her hands in her pockets and leans back a bit, looking Amy over. It’s a friendly enough look, but Amy bristles a little even so. “What happened? Did you turn him down when he asked?”

“No,” Amy says, her throat tight. “He left me here.”

The woman’s smile disappears, eclipsed by an old, ragged pain — a wound well hidden, but still raw. Amy looks away quickly, embarrassed for her. She wouldn’t ever want someone to see something like that in her eyes.

The woman laughs again, but there’s little humour in it. “He does that. Even when he doesn’t mean to.” She rubs a hand over her face, and when she lowers it her expression is perfectly composed again. “Bad habits, you know. He’s not what you’d call trainable.”

The front door of the house closes, and a moment later Rory shuffles through the winter-brown arbour. He’s tugged an old jumper over his dressing gown, and he squints at them in the darkness, sleep-ruffled and resigned to whatever madness the night may bring. “Amy,” he says, voice still a little rough from his latest cold. “Who’s your friend?”

“Haven’t asked yet.” Amy turns to the woman. “Who are you?”

The woman bites her lip. “I don’t usually give my name. For safety reasons.”

Amy turns back to Rory. “She’s the Doctor’s ex.”

“Well, then,” Rory says, apparently unfazed, “you should probably invite her in for tea. It’s bloody freezing out here.” He turns around and shuffles back into the house. The front door closes behind him with a click.

Amy tosses the truncheon behind a bush. “Do they drink tea in the future?”

“God, yes. They practically live on it.” The woman looks back at the shed. “How long–”

“About nine months,” Amy says. “He destroyed the old shed, said he’d be back in five minutes, and showed up twelve years late. Then he saved the planet from an angry horde of eyeball aliens and disappeared again. You missed him by nine months.”

“Well,” the woman says, expressionless. “Isn’t that just typical.”

“Yeah,” Amy agrees. “He’s sort of a prick.”

In the kitchen, Rory’s already put on the kettle. He sits slouched at the kitchen table, a packet of biscuits open in front of him. Amy sits beside him, rubbing her hands together as feeling slowly returns to her fingertips; the woman lingers in the front hall, frowning.

“Your house,” she says. “It’s really…big.”

“Um. Thanks?” Amy gives in and sticks her still-freezing hands up the back of Rory’s jumper. He flinches, and her fingers begin to thaw. Much better.

“How many people live here?”

“Just me,” she says. Rory coughs, and Amy rolls her eyes. “He visits. Mostly for sex.”

Rory shakes his head. “That is — so unfair. And inaccurate. And insulting.”

The woman drifts into the warmly lit kitchen, and for the first time Amy sees her properly, without shadows. Her age is still hard to guess; she looks as if she should be in her mid-twenties, but there’s something older in her eyes and the sharp lines of her face. In the dark her pale face and hands had seemed haunting, almost romantic — now she looks fragile and grey with exhaustion.

“You’ve been ill,” Rory says. It isn’t a question. He stands, and Amy’s hands slip out of his jumper. “Sit down — I’ll get you some water. How long has it been since you’ve eaten?”

“I’m fine,” the woman says. She watches curiously as he fills a glass from the pitcher Amy keeps in the fridge, as if she’s observing firsthand some strange alien ritual she’d only ever read about. “Had some trouble lately finding safe places to rest. I’ve been travelling.”

“In time?” Amy asks.

“A bit,” she says. “Usually not on purpose.” Rory gently crowds her into a chair and sets the glass of water in front of her. She nods her thanks. “Mostly I’ve been universe hopping. Now I’ve got the right universe, but I can’t seem to find the right place or time. I’ve been chasing ghosts.” She gives Amy a tight smile. “I probably shouldn’t tell you much more than that, really. I probably shouldn’t talk to you at all.”

“Is that why you don’t give your name?” Rory asks. “Because you’re afraid of creating a paradox?”

“Someone’s been doing his research,” the woman says, and for a moment there’s something warm and almost flirtatious in her tone. Amy doesn’t like it. At all.

She leans forward, her elbows on the table. “Are you from a different universe, then? How different is it? Are you even human?”

The woman blinks at her. “Would that matter?”

“Of course it matters,” Amy says. “Last time I met an alien it had a face like Satan’s goldfish. If you’re hiding a mouthful of steak knives, I think we have a right to know.”

Rory frowns. “Amy–”

“No, it’s all right,” the woman says. She meets Amy’s eyes with a steady gaze. “I was born in this universe, in London, in 1986. Both my parents were human.” She pauses. “As far as I know. People sometimes wonder about my mum.”

“People sometimes wonder about Amy, too,” Rory says, and neatly dodges Amy’s kick to his shin. He pushes the packet of biscuits in front of the woman, fussing like someone’s mother. “You should eat something. I could make you a sandwich, if you like.”

“Tea will be plenty, thanks. I can’t stay long.”

“No,” Amy says, before she even realises she’s opened her mouth. “You’ll stay here tonight. Get some sleep.”

The woman looks as if she’s about to argue, but just then the kettle starts to whistle, high-pitched and piercing. The woman flinches, one hand moving reflexively to her jacket pocket. Then she stops. Settles her hands palm-down on the tabletop. “Thanks,” she says. “It’s been a while since I’ve slept.”

Rory makes the tea — the woman takes hers with two sugars, no milk — and then sets a mug down in front of each of them. “Right,” he says. “I have work tomorrow, so I’m off to bed.” He drops a kiss on the top of Amy’s head. “I’ll make up the bed in the spare room, all right?”

“Yeah, sure,” Amy says, watching the way the woman curls her fingers around the solid heat of her mug. “Night.”

Rory’s walking away from the table when the woman catches the sleeve of his jumper. He stops, startled, and she tugs him down to whisper something in his ear. Rory looks once at Amy, his eyes a little wide, and then he nods. Amy sees the slow start of a smile on his face as the woman lets go of his sleeve.

“I suppose I’ll see you both in the morning,” he says, and disappears up the stairs.

Amy levels a glare at the stranger in her kitchen. “What did you say to him?”

“Nothing important.” The woman shrugs. “Just something a friend of mine says he wishes someone had told him after he first met the Doctor.”

“Yeah?”

“Yeah,” the woman says mildly, and takes a sip of her tea.

For a moment Amy wishes she hadn’t thrown away the truncheon. She taps a long, green-varnished fingernail against the tabletop. “Did you travel with him, then? In that blue box?”

“For a while,” the woman says. “A long time ago.”

Amy nods. “And then he left you behind.”

The woman’s knuckles turn a little white where they grip her mug. “He didn’t have much choice at the time. Neither did I. There was a war, and we were separated.”

“But he isn’t looking for you,” Amy says. “You’re just looking for him.”

“I’m not looking for him because I miss him,” the woman says, a sharp note entering her even voice. “I need his help. So do you, come to think of it. We all do.”

Amy snorts. “Please. You make it sound like the world’s going to end.”

The woman gives her a dry look.

“Oh. Right.” She lifts her mug and takes a long drink. Swallows. “Jesus.”

“I wouldn’t worry about it,” the woman says. “It happens more often than you’d think; I’m sure we’ll sort it out eventually.”

Amy doesn’t like being wrong about people; it makes her stomach ache, and it happens so rarely that she’s never really learnt what to do to make it go away. She leans forward, her arms folded on the table. “I want to help. What can I do?”

“You can help me find him,” the woman says. “You can tell me everything you know about what he was doing here and where he was going.”

And she does. She starts at the beginning, with the night the blue police box fell from the sky. She tells the woman about the apple and the yoghurt and the beans, about fish fingers and custard and the single, searching blue eye hidden behind the crack in her bedroom wall. The woman listens silently as Amy goes on about cricket bats and handcuffs and the shocking, flesh-and-bone weight of a figment of her imagination, of her Raggedy Doctor made real again — about Prisoner Zero and coma patients and the way the sky went dark when the Atraxi sealed them away from their sun. The woman believes every word of it, without question or confusion or doubt, and when Amy’s done she simply nods and says, “Do you have a picture?”

“Sort of,” Amy says. She get up and fetches her bag from the cupboard in the hall. There’s a sketchbook inside, one she rarely lets anyone see. She flips to the last page and shows the woman the only picture of the Doctor she’s drawn since he stumbled back into her house twelve years too late.

She’s drawn him handcuffed to her radiator, awake and furious and waving the little blue pen-thing he’d called a sonic screwdriver, whatever that means. He looks as raggedy as ever, his pinstriped trousers ripped and fraying at the knees and too-long hair spilling into his eyes. It’s a good likeness. The best she’s ever done.

The woman looks at it and all the colour leaves her pale face.

Rory would probably leap up and take her pulse or something — speak in a soothing voice, tell her to put her head between her knees and breathe. Amy doesn’t know how to do that, so she reaches across the table and takes the woman’s hand.

“I was wrong, before,” the woman says. “When I told you I was sort of from the future.” She closes the sketchbook gently and pushes it back across the table. “I’m definitely from the past.”

“I’m sorry,” Amy says, though she isn’t sure what she’s sorry for. She just knows she is.

The woman stands, abruptly. “I shouldn’t be here. I need to go. I really–” She covers her eyes with her hand and just shudders, like a tree bending against the wind. When her hand falls, there’s nothing old in her eyes at all. “I don’t belong here.”

“It’s my house,” Amy says. “I think I’m the one who decides who belongs and who doesn’t.” She follows the woman out of the kitchen and into the shadows of the front hall. “It’s my house, and I want you to stay.”

The woman turns into her, turns and looks up to meet her eyes. “He’s a terrible driver,” she says. “Couldn’t find his own birthday if you gave him a calendar with the date circled twice and marked with a bloody star, but it’s not because he doesn’t try. I know it seems like he can do anything, like he’s the most amazing man anyone could ever imagine, but he isn’t a dream and he isn’t anyone’s imaginary friend. He’s infuriating and imperfect and more than a little mad, and I promise you he’ll come back for you if he can.” She reaches for the doorknob. “But don’t wait for him, Amy. He’s not the only wonderful thing in the world, and if you’re looking for him you won’t see anything else.”

Amy lifts her chin. “I suppose you’d know.”

“Yeah,” the woman says. “I suppose I would.” She opens the door, and a gust of cold air escapes through. “Goodbye, then. Tell your friend I said thank you.”

“I hope you save the world,” Amy says. “Whether you find him or not.”

The woman grins. “Oh, I’ll find him. I’m not the sort who gives up easily.” She steps through the door and slips her hand into her jacket pocket. “I have a feeling that’s one thing you and I have in common.”

The woman walks away, her footsteps loud against the pavement stones. Then suddenly a flash of light enfolds her, a slow crackle of lightning in shades of blue, and when it fades into darkness it takes the strange woman with it. She’s gone.

Amy closes the door behind her.