Jo nodded. “He was watching you. Two years before you were given the flat, around the same time he took over Franks’ life, he hacked into the council system to prevent anyone from renting it. He must have known that the housing people would notice the glitch eventually. So at some point in those two years, he fitted the spyware. I suppose, if a random stranger was going to be in a position to be observing him, he wanted to be watching them first.” Or maybe, and Joanna thought this more likely, he did it initially to amuse himself. One thing she knew from the many psychopaths she’d encountered over the years was that they tended to get bored easily. The crimes they committed had to get steadily more disturbing each time, ramping up the level of violence or deviance in order to achieve the same thrill.

“All those hours of practice, when I thought no one was listening. I never realized until he mentioned a piece I’d written that I’d played in the flat but never played him. After that I spotted three tiny cameras. There was even one in the bathroom.”

“Don’t think about it too much. You’ll drive yourself mad.”

Ruby’s hand flew to her mouth. “Oh, Jo, no one from the police had to look at that, did they? You didn’t—”

Joanna shook her head. “You don’t have to worry. We’ve destroyed the footage.”

“What really puzzles me, though, was that he knew so much about classical music. We talked for hours about the vagaries of Brahms or which was our favorite Schubert lieder.”

“I guess he was genuinely a fan,” said Joanna.

“I don’t know if he was genuinely anything. He’d certainly done his homework, but there was this Mozart thing that he thought I’d written … doesn’t mean much. I guess I’m just going over everything he said to me in the early days, and wondering how I fell for it.”

Jo opened a bottle of red to let it breathe. “I shouldn’t tell you this, but we’ve found his fingerprints at crime scenes in almost every county. Mostly house burglaries, dating back ten years. One or two very odd ones, though …”

The frightened look on Ruby’s face made her stop, then, before she got into the story behind the preserved finger from the metal box and how it led them to discover the dead man’s identity. As she poured the wine, Jo kicked herself for oversharing; she ought to keep in mind that gory details are not for everyone. In a similar way to the psychopaths, she’d become immune to horror: over the years it took ever more violence and deviance to shock her. This, however, was nothing ordinary, a case she would remember for a long time and one she thought she would never cease to be sickened by.