Dedicated to the three teachers who taught me how to write over the years — Sylvia Clark, Eve Wilson and Iris Cannon — and also to the four writers whose work has acted as living tutorials for me — Stephen Gallagher, Tim Powers, Jonathan Carroll and David Morrell.

And with grateful acknowledgements to:

Marc and Cat Dimmock, for encouraging me; Stella White, Michele Fry, Scott Fraser, A. Kinson, Chris Chalk, Susan Belcher, L. M. Cowan, L. Hay, Stuart Bentley, Mandy Nolan, D. J. Mann and all the other people who wrote reviews of the first Young Sherlock book for Amazon at exactly the time I needed to feel better about writing, and Dominic Kingston and Joanne Owen at Macmillan for looking after me in such a great way. Thanks, everyone.

James Hillager thought he was hallucinating when he first saw the giant leech.

The Borneo jungle was so hot and so humid that walking through it was like being in a Turkish bath. His clothes were sopping wet, and there was so much water vapour in the atmosphere that the sweat wasn’t even evaporating from his skin: it was just dripping from his fingers and his nose, or rolling down his body and collecting wherever his clothes touched his flesh. His boots were so filled with water that he could hear a squelching sound whenever he took a step. The leather was going to rot away within a few weeks if this kept up. He had never felt so miserable and uncomfortable in his life.

The heat was making his head swim, and it was that — and the fact that he was dehydrated and he hadn’t eaten properly for days — which made him think he was hallucinating. He’d been hearing voices in the trees around him for some time now: whispering voices that were talking about him and laughing at him. Part of his mind was telling him that it was just the sound of the wind in the leaves, but another part wanted to yell back at them and tell them to shut up. And then maybe shoot them if they didn’t obey.