There is a killer loose on the London underground. He kills without leaving any forensic trace, and seemingly without motive. When Reuben Maitland discovers that his long-abandoned work on Behavioural Profiling, to predict latent homicidal behaviour from people's DNA, is being put back on track at his old unit GeneCrime, he knows he has to act. Only Reuben knows that the Behavioural Profiling technology is dangerously flawed, and innocent lives are threatened. But what he cannot know is that his investigation will lead him directly into the path of the underground killer.