She lay her head on his right shoulder, smoothed her right hand over his t shirt. "This is just lust," she said.

"Desire," said Leo.

They had kissed a long time, and now lay sprawled on her coat. His arms were strong around her, and he breathed slow and steady beneath her cheek.

"Same thing."

"No, it's not." He squinted down at her as she raised her head. "You can desire a person's mind as well as their body. It's bound together."

"Blimey, get you, Oprah."

"The body thing is kind of secondary," he said. "For me."

"I get that," she said.

"I'm not saying I don't want to -"

"I know." She rested her hand on his belt buckle. "Everyone's different," she said. "Just because popular culture says all blokes must be sex maniacs, doesn't make it true."

"I don't want the sex thing to interfere with the mind thing. Working together."

"Me neither. Anyway, I hardly ever see you. It's not like you're going to stop work and just spend all day in bed with me."

"Doesn't sound that bad actually."

"Tough. I have a dissertation to write." Her hand roved away from his belly, cupped the wound in his side.

"Does it bother you?" he said. She felt him hold in his breath.

"Yes," she said. "Not enough to stop me though. -Everybody has stuff. You know. Stuff with their bodies, stuff with people in their past." His breath eased out. She kissed his neck, tasted salt, and soap.

"I don't have much of a past," he said. His fingers explored the denim over her hip.

"I worked that out."

"I'm quite interested in getting one."

She levered herself up to look him in the eye. "OK."

"That's it? OK?" He found her free hand and clasped it, as if seeking confirmation, a positive connection.

"Yup."

"Oh. Ok."

Once the moment of decision had passed, that they were going to do this thing, everything changed. The cold draught and the scratchy, hard carpet tiles were disregarded as they kissed again and inched slowly closer and closer until they were nose to nose on the floor, with 823 English Literature looming over them. She shrugged off her big sweatshirt, and he began unbuckling his belt. She stopped him with a look, and did it for him.

He took the help, and leaned back luxuriating in the attention. She was a little slow over it, letting her hands rest on his waist, his hips, then on his thigh as she dragged the belt away.

His eyes were bright. Keeping eye contact, he unfastened his jeans button.

She bent over him, kissed his lips, and they lay pressed together, mouths joined as her hand slid down the zip. He was hot, and she felt his reaction to her touch, under her fingers, in his kiss.

Escaping jeans is rarely graceful. They giggled as he wrestled with his while still trying to hold onto her. When the denim finally skidded towards the skirting board, his hands were already in the small of her back, his fingers working into the waistband of her skinnies. "For comfort," he said, tugging on them.

"Comfort, right," and the giggling began again.

They shimmied under the cover of his shirt and there she was, half undressed and alone with him and everything was perfect.

She pried off his t shirt. The port was obvious even in the dim light. Fear bloomed in his eyes as he caught her looking. "It's OK," she said. "You are you. That's all."

"Are you sure it's not the difference that interests you?" His voice was heavy and casual, fake casual like throwing on a duffel coat over a tuxedo.

"I didn't know you were different when I met you," she said, diplomacy working at full throttle. She trailed her hand over the dark hair on his chest. "And then... I just liked you. It was too late."

She felt some of the tension sink from his body. She covered his heart with her hand. His life beat fast under her palm, his second life, his changed brain. She could not compare their joined pulses: her imperfect data capture, versus the fact that he was helplessly recording this. "I'm sure," she said.

He ducked his head, ran his hand over her ribs, her waist, then inside her t shirt, and over her belly, then breasts... He raised his eyes to hers again. "I'm sure too. - I can't believe how beautiful you are."

The compliment was nice but his touch, tentative under her t shirt, was infinitely better. She pulled his hand around to the front fastening and drew in a sharp breath as he slid off the bra. He caressed her through the soft jersey of the tee, watching her reaction, not stopping her hands which were likewise drinking in his chest, his skinny waist, his hips and groin.

"It's not fair," she said. "You can play back everything later."

"I think this," as underwear was thrown aside and he fitted himself against her, "will instantly take the number one spot."

She batted him. "Have you got...? I mean I have, somewhere, but I'd have to go and look..."

"That's good to know," he said, fishing a packet from his jeans pocket on the floor. "I mean that you don't expect..."

"Yeah, stop talking now."

"Good idea."

"What does it say about you that you did expect," she said, to break the ice as the cold plastic packet landed on the sweatshirt between them.

"That I'm a hopeless optimist."

"That's an oxymoron."

It struck her later as odd that he was prepared. Because that meant that the original Leo had been prepared. But now was not the time, and her slightly greater expertise was needed. "Can I..."

"God yes."

She draped herself usefully over him and kissed his lips. "I want you," she said. "Here with me right now." Her hand showed him her meaning, trembling because he was not just some boy, he was Leo. "I love you," she said, and was amazed as a tear fell from her eye.

His thumb brushed her cheek. "We can stop if you want."

"What? No!"

"Then..." He rolled her sideways, pulled up her tee and began kissing her breasts, one hand helping with that while the other slid along her thigh. In two seconds she had forgotten her tears and was saying, yes, now, more. He became fierce, but it was good, and where she thought she would need to lead, he matched her boldness with his own eager touch.

It didn't last long, for him, and he lay in her arms afterwards, not speaking, just breathing and staring at the shape of the lights on the ceiling, until at last he turned to her and kissed her, a reverent kiss like a thank you, like a full stop. She thought she was going to have to be blunt, but no, he manoeuvered to one side and used lips and fingers and hands until she was melting into him too, her kiss drowning his and her gasps drawing out a fresh reaction from his body.

After a while the room simmered down a little and became again just the cold hard floor of a public library. "Oh my God," she said. She turned her head to look at him and found him already gazing intently at her.

"I love you," he said.

She smiled, and began pulling on clothes, shivering as sweat began to dry. "I love you too," she said. "And him. But definitely you, since you're here."

"Mattie." He caught hold of her hand and kissed her fingers. "It's me."

She stared at him. His fingers entwined with hers suddenly made no sense, the connection they'd shared suddenly broken.

This was more difficult than he'd thought. "I have my memories," he said.

Her first instinct, as usual, was defensive snark. "So this was a bad novel all along? Magic sex, my secret superpower..." She freed her hand and began pulling her shirt sleeves the right way out, her hair falling over her face.

"No." He leaned forward, trying to catch her eye. "It was before. When I was reading. Your idea ... either it worked, or more likely, it just took longer than we expected for my system to run a full cycle of memory reattachement."

"So..." She was looking highly unimpressed. "You just pretended to be... him. No-memories you."

"I am him."

He watched her think about that as more clothes went on. He was not surprised when her next question was practical: she and he were alike in so many ways. Mattie looked him in the eye, as fearlessly as she had when they were skin to skin, and said, "So now what?"

It was a good point. He had thought and thought about it, for months, ever since she first let him know that she liked him. That miracle itself took a long time to process. Even after he was sure what he wanted, there was no obvious next step except the one they had just taken. And even after that, the question remained, and she had come straight to it: just like her. "Well," he said. He swallowed. "Whatever you want."

"Hmmn. Not to accuse you of a cop out, but..." Knowing it was him made things different, even though he was still half dressed. She felt a strange embarrassment, that Leo, her Leo, had witnessed all that... But then, he had initiated it too. "I'm not seeing a big white wedding, if that's what you're angling for."

That made him laugh, and she kissed him, knowing it was him, with all the tenderness of a first kiss, which she supposed it was. Then she said, "I know what's next."

He was right there too. "More work," he said. "Now we know some more of my Dad's secrets."

"Yes," she said. "Now we know the interface."

She reached for her jeans but was stopped by his arms around her waist.

"Since we're here," he said, and raised one eyebrow.

"You're on half charge," she said.

"Yeah?" said Leo. "You sure about that?"

"Oh my god," she said, "synth humour," but her laughter was smothered, willingly smothered, by his kiss.