Reuben Maitland is a forensic scientist forced to work outside of the law. Fired from his job with the CID, he takes work where he finds it. But when he 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. Rogue elements within GeneCrime believe that prevention is better than cure, and are using Reuben's research to hunt down and incite innocent people beyond their breaking point. Reuben turns to the one person in GeneCrime he can trust, DCI Sarah Hirst. But the GeneCrime unit is frantically trying to stop a seemingly invisible killer who strikes in the middle of the day on busy Tube lines. As the bodycount escalates, London life threatens to grind to a halt and panic begins to rise.Drawn back into GeneCrime by his feeling for Sarah Hirst, Reuben starts the hunt for the people misusing his technology. Only Reuben knows that the Behavioural Profiling technology is dangerously flawed, and innocent lives are threatened. But what he cannot know is that this hunt will lead him directly into the path of the Underground Killer.