One question binds these and many others from the casebook of Britain’s leading forensic psychiatrist: Why? What drives a person to commit seemingly inexplicable crimes?

Dr Duncan Harding is the person the police and the courts turn to for answers – to establish a defendant’s mental state and motivation: their fitness to stand trial.

It is a career that has brought him face to face with psychopaths, taken him to the limits of human compassion and to the darkest corners of his own troubled past.