There is a killer loose on the London Underground. He kills without leaving any forensic trace, and seemingly without motive. 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. Now rogue elements in the police, believing that prevention is better than cure, are using Reuben's research to hunt down and incite latent psychopaths beyond their breaking point. Reuben must track down whoever is misusing his technology 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.