Then he heard the noise again. It was a kind of scratching sound. And it was behind him. He whirled around, and then looked up the stairs. Staring at him from the top was Napoleon, Trish’s dominant ginger and white cat, kneading the carpet. Furious that the animal had got in, but unwilling to wake Sam, Gillard crept up the stairs towards it. It darted away out of view. He had been meaning to put a wire mesh across the casement window, but hadn’t yet got round to it. He looked in the spare room; the window was closed, as it should be, and there was no sign of the cat. That left only their bedroom, the main bathroom or his office. He checked the last first, and it was clear the cat had been in there, because papers about the Roy case had been pulled off his desk, scrunched up and clawed. He could almost believe the animal could read. There was also a vile stink. The offending deposit was on the carpet just below his desk.

‘You’ll regret it if I catch you,’ Gillard hissed. The cat was not in the bathroom, so it must be in the bedroom. He crept back and saw it, as bold as you please, standing on the corner of the duvet near his wife. He reached out, but it jumped off the bed and dodged past him and downstairs. He could hear Sam now, awake and calling out, but the hot pursuit of the cat took precedence. He thundered down the stairs, and saw that the internal door from the utility room to the garage was ajar. He grabbed a torch from the telephone table and went into the garage. He shone the beam across the darkened space, then saw that the small side window looked to be the cat’s entrance point. It was less than a foot across, and five feet off the ground, but the wood was rotten and one part of the cracked glass looked to have fallen and shattered. As he crept further into the cluttered garage, Napoleon jumped out from behind some bags of fertiliser, leaped onto a small shelving unit, and then with acrobatic aplomb scrambled the final two feet up the wall, and through the broken window.

Gillard swore softly. A ruined night’s sleep ahead of an early start tomorrow. Ashtead Common for a re-enactment of Mrs Roy’s last dog walk. Rigby had got her way.

The crime scene reconstruction was a washout. The idea of a re­enactment was to prod memories. But heavy rain and – because of the early hour on a Sunday morning – a paucity of spectators contrived to make it seem a waste of time. The assailant, played by Ryan Jones, a young CSI trainee in Kirsty’s class, managed to fall off his bike, twice. Bertie the boxer dog seemed confused and lethargic, unwilling to run for the balls thrown for him. When the middle-aged Asian woman playing Mrs Roy gamely threw herself into a puddle after the mock attack, Bertie simply wandered off rather than guarding her body.