“There are six,” he said. “And they alternate from camera to camera. Which means the odds are against your showing up on screen at any given time.”

“So they don’t automatically detect motion?”

“Maggie.” He had reached across the table and put his hand on hers. Around them had been the usual clatter of young mums and earnest hipsters: like most of their conversations, this had taken place in the café where they first met. Where he had first approached her. “It’s fine to be scared. It’s fine not to want to do this.”

“I do want to do it.”

“And I wouldn’t ask if I could see any other way of getting the job done. If you knew—”

He broke off while a young woman squeezed past with a tray piled high with dirty mugs, their rims laced with froth.

“I know you wouldn’t,” she told him.

Because she was his only hope.

Her wristwatch pinged when midnight struck.

For a moment, the sound confused her—she had not been asleep, precisely, but had entered a fugue state in which memories and plans collided, throwing sparks off each other—and she jerked upright, banging her head against the cistern. An image of her sister popped and vanished as the cubicle light flickered on, followed by the other bulbs in the lavatory. Her heart pounded. Someone would come. But nobody did, and after a moment Maggie unfolded her limbs, which were creaky with cold, and tried to rub life into them.

Pins and needles assaulted her fingers. She did not feel like an agent on a mission. She felt like a young woman up past bedtime, who wanted only to crawl beneath some covers and find warmth.

“What do I do now, Harvey?” she whispered.

It would have been nice if he’d been there, offering an answer. But it was up to her now. She was on her own.

Because it didn’t matter—because the lights had blinked on anyway—before making her way out of the cubicle, she raised the toilet lid, pulled down her jeans and pants, and used it for the purpose for which it was intended. Then she rearranged her clothing, closed the lid, and had her hand on the handle before she caught herself—that would be all she needed, to send a watery alarm cascading through the building. She imagined security guards stomping up and down the stairwells, crashing into the lavatories on each floor, throwing open doors, looking for the culprit.

“Maggie, Maggie,” she murmured to herself.

When her heart rate was normal she unlocked her cubicle and tiptoed to the door and opened it and peered out.