“One last thing,” said the DI, fixing Joanna with a steely eyeball. “Don’t try to charge my investigation with any more MRI scans. Unless you want to pay for them yourself.”

“Yes, sir. Sorry, sir.”

She drove back to the police station, the police radio turned up so she could monitor the search. By the time she’d parked and made her way to the incident room, she was feeling despondent about their chances of catching him. There’d been no sightings whatsoever since he’d escaped from the ward. It was as if he were the Invisible Man.

In the incident room, Eddie was waiting with news of the search for Constance B and Leonie. Like the doctor, he’d been up most of the night, and it showed.

“Hi, Eddie. Did you find them?” Joanna struggled to control the slight tremor in her voice. If they’d found Ruby and Leonie, at least she’d have a chance at getting to them first, at keeping them safe from the fugitive.

“We checked CCTV at the Edinburgh train station, where their journey was supposed to end. There’s nothing. She didn’t get off there. So, we’ve had to search cameras at every stop on the line, but I’m afraid to say, it’s not a straightforward process. Some of the systems are still analog. We’ve been uploading all the tapes and programming the face-recognition software to search. It all takes time. As a result, we don’t have anything yet, I’m afraid.”

“How long until you do?” said Harper.

“Maybe another couple of days.”

“Can’t you make it happen quicker?”

“I’m afraid not. Today we’re having the tapes couriered over, but getting them into our system is a bit of a laborious task, as you can imagine. We have to convert them to digital in real-time, and then—”

“Well, get some more people on it, can’t you?”

“There isn’t anyone. And I’m going home.”

“Can’t you stay? Do a bit of overtime?”

“No,” said Eddie. “In case you haven’t noticed, I’ve done ten hours overtime already. And tomorrow’s Christmas. My annual leave started yesterday; I should be at home relaxing by now.”

She thought about ramping up the pressure, letting him know just how urgent it was. Maybe she could try yelling at him. But there was no point burning bridges that might be useful in the future, if she could help it.

“Fine,” she said. “You go home and have a break—you deserve it. But if you could do one small, tiny favour for me before you do.”

“What is it?”