The bed was rumpled but the sheets had been recently changed and the duvet laid out and turned back. There was a pile of books on the bedside table – art books but of the serious academic kind rather than the coffee table variety; on socialist realism, propaganda posters of the 1930s, classic London Underground posters, and a volume called Right About Now – art & theory since the 1990s. The only non-art books were an omnibus edition of Colin MacInnes’ London trilogy and a reference on mental health called 50 Signs of Mental Illness. I picked up the medical book and dangled it by its spine, but it stubbornly failed to reveal any tell-tale gaps where it had been heavily read.

Looking for material? I wondered. Worried about himself or somebody else? The book was still crisp and relatively new. Was he worried about Zach perhaps?

I looked around the room, but there were no books on the arcane or even the vaguely mystical and not even a vestige of vestigium beyond the normal background. This is a classic example of what I was coming to call the inverse law of magical utility – in others words the chance of finding magical phenomena is inversely proportional to how useful it would be to bloody find it.

It was entirely possible that any magical side to the murder rested with the killer, not the victim. I probably should have stayed in the tunnels with Sergeant Kumar and the search team.

So of course I found what I was looking for five minutes later, downstairs, while we were statementing Zach.

Zach had put on a pair of tracksuit bottoms and a T-shirt while I’d been upstairs. He was sitting half hunched over the table while Carey took his statement. Guleed had taken a position leaning nonchalantly against the simulation farmhouse kitchen unit just inside Zach’s peripheral vision. She was watching his face carefully and frowning. I guessed she’d spotted the mental health book too.

There was a cup of coffee waiting on the table for me. I sat down next to Carey but kept my posture relaxed, took my coffee and leaned back slightly as I sipped it. Zach’s hands were trembling and he was unconsciously rocking back and forth as we went through his movements in the last twenty-four hours. It’s always useful to have your witnesses a little bit unnerved, but you can have too much of a good thing.

On the table was an earthenware bowl sitting on the kitchen table with two apples, a splotchy banana and a handful of minicab cards inside it. It was the same rich biscuit colour as the shard I’d found in the Underground but too curved to be an identical piece.