There is a killer loose on the London Underground. He leaves no forensic traces, and Genecrime, the UK's elite forensic unit, are stretched to the limits trying to find one usable clue. And there is another problem facing Genecrime. Before he was sacked as head of the unit, Reuben Maitland developed a system to predict latent homicidal behaviour from people's DNA. Someone is misusing his technology and Maitland must track them down and stop them before more lives are destroyed. But what he cannot know is that his investigation will lead him directly into the path of the Underground killer.