She's twenty, or thereabouts, carrying herself with a confidence that slips only slightly into arrogance. She's worked out how much smarter she is than most people, and doesn't remember the only person she ever met who could (sometimes) beat her at chess. Her hair's longer now, and her body has filled out in ways that he finds far too inviting. When she smiles he can still see the girl who became this woman, a memory still far too clear after centuries.

"Zoe," she says, offering her hand. It's warm and it takes him back to holding that hand and running towards danger.

"You've got lovely skin," he tells her. "The hands of a mathematician."

"Astrophysicist," she grins. "I'm studying coronal activity during sunspot minimums."

She's wearing something skintight and glistening, made to catch the eye and guide it to the wearer's curves. She giggles when he stares and the movement travels across her body.

People are so casual in this time. "Do you want to go somewhere?" he asks, and fights down the urge to take her far, far away from here. It's Zoe, who doesn't remember him, and he shouldn't keep dragging people from their lives.

As if that ever stopped him before.

She shrugs herself out of her clothing in a white-walled bedroom that looks as sterile as the rest of this time. A computer terminal runs numbers on solar flares as the only proof that anyone's ever spent any time here.

"You remind me of someone," she says, "but I can't for the life of me think who it is." She shakes the thought from her head. "I had a medical yesterday. No infections and I topped up my contraceptive dose." She looks at him expectantly and he nods and professes his lack of disease as he fumbles with the laces on his trainers.

“Very retro,” she says, folding his jacket over a white plastic chair. “I heard that was fashionable in the northern hemisphere these days. Not very practical, but I like the fabric.”

“Zoe,” he says, “you have a mind like a computer.”

She laughs, takes it as a compliment and settles herself on the bed, propping herself up on an elbow to watch him undress. Always one for details, his Zoe, always absorbing information.

“What do you do?” she asks.

“Oh, this and that. I saved the world last week, all on my own.” He lies down next to her and traces his fingers over skin pale from too many years indoors. “You should get out more,” he says, “you should see this universe you live in. You’re only young once.” He was young himself once, and Zoe doesn’t remember any of it.

She thinks he’s hilarious. “You have regressive tendencies,” she laughs. “Don’t worry, I won’t tell anyone.”

He lapses into silence, following the urge to explore as he learns her body. It never mattered when he knew her heart, but this Zoe isn’t his, this Zoe never saved his life or helped him chase the monsters away. For a moment he ceases to be gentle, bites on skin to leave a mark on her inner thigh. Just to prove he’s known her, just to make it real. She doesn’t mind, and digs a trail along his shoulder with her nails.

”We’re the same,” he whispers against her skin, “we’re part of each other.”

She looks at him for a moment, clear eyes wide in black outlines. He thinks she’s about to say something, but then her arms wrap round him and she pulls him into her and this is as much as he can ask for.

Afterwards he holds her until he can talk himself into letting go. Then she’s up and tidying, handing him his clothes and he resents this Zoe, just a little.

“Will you remember this?” he asks, suddenly afraid.

“I remember everything,” she says, “eidetic memory.”

“Do you remember --” he starts, and presses on before he can change his mind. “Do you ever remember anything that can’t have happened? Being places you know you’ve never been? Stuff like that?”

“I have dreams sometimes,” she says, as though sharing a secret. “Strange ones, about things I’ve never seen. They should be frightening, but… they’re not. I always feel safe.”

“Other lives,” he says. “Adventures you’ve forgotten about.”

“You’re very unusual,” she grins. “Can I see you again?”

He’s tempted. He’s so, so tempted. “I’ve got to get back to saving the world. It won’t just save itself, you know.”

“Of course.”

“You could… you could come with me?” He’s stupid, sometimes. He shouldn’t have asked, because he knows she’ll say —

“No, I’m afraid I’ve got things to do in the real world.”

“I love you, Zoe,” he says. “Everyone should.”

She laughs again, but he doesn’t mind. He can remember for both of them.