This takes place towards the end of series 1, when the synths and Leo are hiding at the Hawkins' house.

Everyone is notionally asleep but in fact the entire house is alive. Mattie can hear gaming from Toby's room. Her parents are talking in low voices in their bedroom, the big light on. Plenty to discuss there and Mattie is impressed that Dad has made it that far. He must have said something really impressive to Mum. Sophie is fast asleep of course, and the synths are dotted around the house at the various charging points.

Mattie pulls on jeans and a sweat top. She can hardly go wandering around in her sleep tee when the house is full of people. She grabs her laptop and earbuds and creeps downstairs in her ironic teddy bear slippers.

Leo has the sofa in the lounge, so Mattie heads for the kitchen. Cup of tea, toast, stare at the internet until she feels even slightly sleepy. In theory the blue light from the screen will screw with her diurnal rhythm, but to be honest at this stage it hardly matters.

She flicks the kettle on and stands by the sink looking out at the garden. It's black out there of course but the solar lights along the path give a faint glow, nothing like the box suggested (a string of bright globes lighting up a group of goodlooking friends for late night outdoors socialising) but enough to see the shape of the garden, the idea of it and what it might, with daylight, become.

In the darkness beyond the glass she sees movement, and jumps. She clutches the edge of the counter and Leo is outside the kitchen door, in t shirt and jeans, socks. His hair is wet. He turns the handle quietly and comes in. Mattie's heart is still racing.

"Sorry, " he says.

"It's all right, "she says. "Want a cuppa?"

"Cheers."

"I couldn't sleep," she says as she fetches down another mug. "You?"

He shrugs. "I just want to be gone."

She focuses on the teabag tin, opening its lid, the hinges squeaking.

He hunches by the fridge. He is so awkward. He obviously knows he has offended her by saying he can't wait to leave her house, but hasn't got the social grace to fix it.

"Scuse." He is in her way.

He edges aside as she yanks open the fridge door. Yellow light brightens both their faces for a moment. "Semi skimmed OK," she says, like a proper hostess. Her mum would be proud, except for the part where her daughter is half dressed in the kitchen at midnight with a scruffy, cyborg man.

Mattie smirks at her own thought and splashes milk into her mug of tea. "Help yourself."

Leo stands beside her at the counter, pouring in way too much milk and then compounding the horror by adding two sugars. He sees her wince and frowns.

"I know," she says. "I don't know you. You said."

"You're looking at me like I'm a specimen of something," he says. "Just - don't."

She presses her mouth shut. She is not going to apologise. She fishes out her teabag and flings it in the pedal bin. He can do his own.

The idea of toast still appeals but not if he is going to be hanging round criticising. She smothers a sigh of impatience and disappointment. He is David Elster's son, literally made of technology. He is clever and a bit sarcastic and a lot cute. He is basically her dream man. So it's a pity that he behaves so much like an arse.

He is watching her again, waiting for her next move so he can duck from it like a prize fighter dodging a low blow. Waiting for the next chance to reject any hint of friendship. She fixes her expression and drinks tea at him, the mug pressed against her chin between slurps.

He lifts his mug, teabag still in. "Thanks for the tea." His bright blue eyes dart to hers and then guiltily away, acknowledging his massive rudeness.

"I was going to have toast," she says, relenting. "If you want some."

"Thanks." His mouth twitches as if he is chewing away a smile.

She untwists the bread wrapper. It crackles like a bad light bulb. "You really don't like people, do you?"

"I don't hate you," Leo says. "I don't despise you. I just don't know you."

"You're not trying, "she says. "We want to help you. I get why you don't trust us. I get it. But..."

"Be nice?" he suggests.

"Would make a change."

He sighs. Notices the teabag still in his cup.

"Oh give it here." Mattie takes his mug and removes the bag. As she gives it back, her hand meets his and a little warmth passes between them, ordinary human contact. She meets his gaze and sees not aggression but vulnerability.

Leo steps back with the tea and sips it. His feet look funny in Dad's socks. He is leaning a little, favouring his unwounded side.

Mattie sighs. He never asked for this, this strange life. He wasn't given a choice, in any of it. "Toast," she says, sliding a plate along the counter towards him.

He looks at it. "Got any jam?"

"What kind?" She opens the treat cupboard.

"Ah... Strawberry. Real jam. Not the seedless kind."

"The seedless kind is evil, "she agrees.

"Like smooth peanut butter."

"And white chocolate Kit Kats." She shudders.

This time he does smile, and she grins too. The kitchen is bright, and Leo Elster cannot hide himself from her, in this or any light.

"I was going to watch a film," she says.

"What?"

"Dunno. Something stupid. Back to the Future?"

He has never seen it. "Go on then."

"If you've already seen a film," she says, "does that mean you never want to watch it again because you can recall it perfectly?"

He shakes his head. "The film, yes. But the experience is different every time. Different places, different people."

"I notice different things every time I watch this, " she says. "I guess it's is a bit like that."

"I don't remember how my old memory used to be. Which is pretty ironic."

They go to the lounge. Leo sets aside the sleeping bag and sits right at one end of the sofa . Mattie takes the hint and goes to the distant other end, placing her laptop on the coffee table in front of them. Mattie plugs in the earbuds and gives him the left one. They slouch against the cushions, the short cable tethering them, limiting the distance that separates them.

Mattie watches the film and also watches Leo, the laptop screen the only illumination the room. About fifty percent of the time, when she sneaks a glance at Leo, he is watching her too.

"Nice slippers," he says when she puts her feet on the table.

"They're ironic."

He snorts.

"I have a sarcastic fist as well if you'd like to see that."

The film is very silly but great. Leo smirks at it, gets up to make them more tea, makes her pause it until he's back. He is sprawled, now, long legs propped on the coffee table, arms loose by his sides, the black T-shirt stretched over his thin torso and the outline of his bandaged wound. His hair has dried and trails onto the nape of his neck. And although dark stubble covers half his face, it cannot hide his smile.

"There's two more," Mattie says.

"I know." He casts her a disgusted look. "I haven't been in prison."

"I mean now." Because she does not want to go to bed.

"Ok."

"Anyway, prisons have the best video libraries of anywhere," she says. "Mum says."

"Good to know for when my enemies catch up with me," he says, his mouth twisting.

"They won't," she says, clasping his arm. "You're too good."

He shakes his head. "I can't do it all alone. But, now I've got them back, I don't have to." The synths are out of sight, but he swivels his head to the study door, behind which Mia is charging.

Mattie removes her hand from Leo's arm, and crouches over the laptop. "I'll find the sequel. Assuming you haven't seen it."

He does not reply. For a few seconds there is only her tappety tap on the keys, her fingers certain even in this dim light.

"Even if I had," Leo says then, sitting up. "I haven't watched it with you."

Mattie glances up and finds him leaning towards her earnestly. She lifts her hands from the keyboard, angling her body towards Leo. A voice in her head is whispering Do it! but his eyes are as wary as they are inviting. She extends her left hand an inch towards him.

"Are you making a move on me?" he asks in disbelief.

Her face burns. But she is no coward and there might not be a second chance. "Maybe," she says. She gives him the Stare of Sass, hoping it hides her terror.

When he continues to gaze at her, offering neither hope nor discouragement she says, "I'll put that film on then."

His hand on her wrist stops her. "We'll stay in touch," he mumbles. "After. Have to be careful though."

"Yeah, my mum would kill me. -Kidding, kidding. Yeah. We'll talk." His fingertips are rough, like the bark of a young tree.

"I haven't got friends," he says. "Just my family." He frowns at his hand on her wrist. "They are my priority."

"It's OK," she says. "I get it." And she does, although it is deflating. He has to protect the conscious synths, and himself, from those who want that technology. Mattie is well aware that in monetary terms, the synths' secrets are worth far more than Leo's life.

He closes his eyes as if his wound has given him a twinge, opens them again. His hand closes over hers. "I'm just trying to explain."

"I know," she says. His hand is warm, his eyes intense. She frees her hand from under his. "Let's watch the film. You don't need to-"

His lips crash into her cheek, his beard soft and ticklish, his hot breath scented with strawberry jam .

"Oh," says Mattie.

Leo draws back looking as embarrassed as she feels. She takes hold of his hand, sets the left earbud into it. -Keeps hold of him after. "Film," she says.

They sit, with his right hand in her left, until both of them have thought about that too much and they ease apart.

The room grows chill as the hour ticks past two. Mattie drags the sleeping bag over their knees. There is no more touching but that's ok, enough has been said to last a while.

"Leo. Is everything all right?" Mia 's voice.

Oh God. Like being caught by your mum. Mattie wriggles further from Leo.

"It's fine," said Leo as Mia appears, a sharp silhouette against the study desklights. "Watching a film."

"Would you like me to watch with you? Hello, Mattie." Mia's eyes are bland but Mattie knows she is recording all that she sees. Like Leo, Mia can't help it, but there's more to it than that: because it involves Leo, Mia will take special note of every detail of this cosy little scene.

"No, go back to sleep," says Leo. Mia withdraws.

"I should go to bed," says Mattie, but Leo is looking at her like a cat daring you to take away its dinner. "Ok, but let's keep it down. Mia's not the only mum with bat-like hearing."

He nods. He pauses the movie. "After," he says. "We'll need a few new usernames. And we need to agree how to start a conversation so we each know it's really the other person."

He is so dedicated. Driven. And right: contact will be difficult, and dangerous for both of them. At least she will be in one place. Who knows where he will be? "I'm going to uni in three weeks," she says. "Southampton."

"Number seven in the rankings," he says instantly. "Their cybernetic engineering department publishes more than all the rest though." She can tell he is impressed. Then he hesitates, looks sideways at her, and then focuses elsewhere: his tell for sharing. She waits, the laptop screen strobing in the background . "I went to St Andrews," he says.

Number one on the list. Of course. "How?" she asks.

"Online course. They thought I was a sponsored management trainee in Korea."

"Shame," she says.

"What?"

"You went to uni without actually going. You never got the full experience." She wrinkles her brow, and her mind fills with all the things you can only do in person.

He shrugs. "S'allright. I was too young to go anyway til my final year."

She rolls her eyes. "Of course you were."

"Yup. Genius, me."

She shakes her head. "Come on. Back to the Wild West."

"Yes, ma'am."

She falls asleep against the arm of the sofa, her ear bud on the cushion beside her cheek. Leo gazes at her. Then he tucks the sleeping bag more securely over both their legs, cradles the laptop and calls up Mattie's work. His eyebrows rise. She is as good as he thought, as he hoped. He starts a new file and begins to type.

When Laura strides in next morning, Leo is flaked out, snoring, his head flung over the back of the sofa, one hand limp on the idle laptop, the other tucked against Mattie's knee. Mattie is curled up on the sofa arm - fully clothed, Laura notes with some relief, because who needs more complications - and she is smiling in her sleep. Both of them look exhausted, like they've been up half the night.

Well, it seems innocent enough, apart from the knee-touching.

"They watched two films and talked until nearly three o clock," says Mia, appearing behind Laura.

"No funny business then," Laura says.

"What do you mean?"

"It doesn't matter. My own dirty mind."

"Mattie suggested they become friends and Leo agreed," says Mia. "They have arranged to chat online and say hey."

"Right."

"They held hands for just over two minutes."

"Right." Oh really.

Mattie opens her eyes, blinks at morning sunshine. Laura retreats into the kitchen, hustling Mia with her.

Mattie slides off the sofa and spreads her covers over Leo. He is out of it. His beard has grown even more in the night. She bends over him. He smells of shower gel, and something metallic, like singed circuits, but it is probably just burnt toast. And he smells warm and sleepy.

"You going to violate me in my sleep?" he says without opening his eyes. She squeaks. "That's very Evil Corp. Very now."

She bats him. "Bastard. I nearly had a heart attack."

His eyelashes flicker. "I'm still asleep."

"Right."

"If you were going to, now's your chance before I wake up and we have to talk about it."

"I think the moment's gone to be honest."

He shrugs. Total indifference. Charming. She bends, meaning to put her freezing cold hand on his neck, serve him right, but changes her mind halfway there. She presses her lips to his left cheekbone, only for a second, but his eyes fly open. His cheek is soft and his eyes, up close, very blue.

He is beginning to be gratifyingly shocked when her mother breezes in saying loudly, "Morning everyone, rise and shine," in that strident tone which tells Mattie that nothing is sacred and there is no bloody privacy in this house.

Well, whatever happens now, at least Leo knows. He's got the choice, which is what he likes, and she has been honest with him, which is the only way she can be. So it's all good, and all the while the group is preparing to leave, Leo is perky with his brother and sister, and extra polite to Laura, and when it is time to go he shakes Mattie's hand and says "Thanks, for the help," and she says, "No problem," as if she is constantly coding and headcracking for fugitive Cybermen. And they exchange a tiny smile and then he is gone.

"I want a word with you," says Laura the moment the door is closed.

Marie smiles at her mother. "Of course you do," she says.

Mattie keeps her promise and waits, as she and Leo planned: a week, a fortnight, a month. The whole family drives with her, the car rammed with stuff, to Southampton. A tiny concrete room become Mattie's home and the wait seems even longer.

At last, though, the agreed date and time arrives. It feels very long since she saw Leo Elster. She trembles as she waits for the site to log her in, but when it does there is a message for her. She launches it immediately and it is from Leo's new username, and it says just, Hey.

She closes her eyes in relief. He is safe and he is here.

You only need a faint glow over the future, not to see the whole shape, but just to give an idea of what is out there, of possibilities. She has been in blackness this whole time wondering, first, if he is OK, and then, if he wants to continue their friendship. And now here he is, just that one word, but it is enough to give their future a little light, to show just a silhouette of what might be.

She takes a breath, settles in front of the screen and types. Hey.