"I want to come with you to fix Fred," Mattie typed. The screen went dark. It was the only light in her cramped student room and suddenly Mattie was surrounded by shadow. She took a sip of Coke and flicked on her desk lamp.

"No way," comes back Leo's message. "Too dangerous."

"I can help! What if something goes wrong?" She put down the Coke can too hard and it splashed sticky brown liquid over the desk. Cursing, she fumbled for tissues and typed one handed as she mopped up the spill. "You know, like Hobb finding you? Like men with guns taking Fred away, killing you on the spot and ripping out your innards? Just off the top of my head."

"Then it will just be my life in danger and not yours. This is not your problem. Fred is my brother."

Oh God, his infuriating sainthood. She narrowed her eyes.

Three hundred miles away in Cumbria, Leo swiped through screens of code on a tablet while he waited for Mattie's response on his laptop. He slurped Red Bull and calculated how late he could reasonably go to bed, given he had to be up for work in the morning.

The pause went on for a while. Leo pictured Mattie resting her fingers on the scratch pad of her laptop , controlling her fury. Then:

"You are my friend," she typed, and he could almost hear the gritted teeth. "I want to help. Would you not want to help if it was Sophie I was rushing off to rescue?"

Leo closed his eyes. Mattie's sweet little sister. If she were hurt or lost-? But she wasn't. It was just an example designed to tug his heartstrings. What was left of them. Leo gulped more Red Bull, then stuck one hand into his kit bag and withdrew it holding his phone. He dialled her number while the question about Sophie still blinked on the screen. "Mattie."

"Hey." Her voice, a little breathless..

"Hey." Their shared call sign. "Please," said Leo. "Just help me by staying behind and not giving me another factor to worry about."

As always, the sound of his voice was an effective weapon against her stubbornness. "Ok," said Mattie. "But I want to do more to help."

Leo paused. He could hear her breathing, and music in the background. She was in her student room then. "Backups," said Leo. "In case anything happens. You can be on standby to do a remote online backup of Mia or Max."

"I don't know how to force a start," she said, and he knew her sharp mind was already whirring.

"I'll show you. I've only just been working on it myself. Trying to rip data from ordinary synths without them knowing."

"Ok," she said. "Show me."

"Not now," he said. "Better get off the line."

"Bye," she said quickly before he could press End.

"Bye," he said, and thumbed the red button.

He lay the phone beside the keyboard. Took a breath and typed. "Hot backups are slippery beasts because the thing you're backing up is a moving target. It's nigh on impossible to get a perfect copy."

"Says you," she typed back. "I've got plenty of experience with the impossible."

He smirked at the screen. "Is that a dig?"

"Only completely."

"You're going to need a lot of memory," he said. "And a protected power supply."

"Hey," she messaged. "You're not the only actual genius around here."

"I know."

"Blimey."

"Sending instructions now. And thanks."

"NP."