Psychopaths have long captured the public imagination. Painted as charismatic, violent predators lacking in all empathy, they provide intrigue and horror in equal measure. But what precisely is a psychopath? What is it that drives them to cause harm, even kill? And can they ever be cured? Presented by psychologist Professor Uta Frith, this is an in-depth exploration of the psychopathic mind - including one of the most notorious of all, the moors murderer Ian Brady. Through an on-going correspondence between the Horizon team and Brady, the film features some of the very last letters he wrote. The film also features a series of candid interviews with prison inmates who not only describe their crimes but why they think they committed them. Horizon explores not only how each individual's crimes were shaped by their own life experiences, but also giving an insight in to how these people think and behave. Working with the world's experts in the field, the film sheds light on the biological, psychological and environmental influences that shape a psychopath. The programme also looks to the future, taking in groundbreaking research that suggests a life time of incarceration is not the only option to manage violent and dangerous psychopaths.