Ruby scrolled through the menu. She clicked on “Locate at close range,” and the screen changed to a set of concentric circles pulsating from a blue central dot. The word in the dot was Receiver.

“This must be the receiver, then,” she said. Next to the receiver dot was a smaller red dot, labeled with the word Locator. At the bottom of the screen, the words Less than 0.5 m.

“That means it’s here somewhere. In the room. You’re sure it’s not in the box? Have a good look, might be stuck on. They’re magnetic, probably.”

Constance ran her hands over the box, inside and out. Nothing. They both looked around them.

Ruby lifted the cushions on the sofa. “How big is the locator, do you think? Did you ever see the one on his car?” She got up and walked across to the bathroom, went inside, and began to feel along the top of the cabinet.

“Ruby,” said Constance. “It moved.”

“What?” She went back into the main room and walked across to where Constance was sitting.

“Stop,” she said, and Ruby stopped. Constance’s eyes flicked between her and the screen of the tracking device. “Okay, go again.”

She’d only taken three steps when Constance said, “It’s you.”

“It’s me? What do you mean?”

“When you went to the bathroom. The dot moved with you. It’s on you somewhere. What have you got in your pockets?”

“Only my phone.” She reached into her pocket and pulled out the phone. “But it’s turned off.”

“Here,” said Constance, taking the phone and handing her the tracker. “Watch the dots.”

Constance walked toward the bathroom. The locator dot moved. The distance marker went up as she got farther away: Less than 1.5 m, Less than 2.5 m, Less than 3.5 m.

Ruby threw the tracker down and grabbed the phone from Constance. She unclipped the back and took the battery out. There was a flat, black circle underneath it that she’d never seen before.

Gregor was tracking her. He’d given her a phone that meant he could follow her every move. She’d been carrying it around, not knowing that at any given moment, Gregor knew exactly where she was. The few times he’d phoned her when she’d been in town, she’d always been at the bus stop by the police station. Not a coincidence, then, as she’d thought; he didn’t fully trust her, suspected she might have been about to betray him to the authorities.