This film examines two of the UK's most dangerous prisoners. Both were skilled manipulators, who used their powers of persuasion to deadly effect.Ernest Wright was a career criminal, whose life on the wrong side of the law was finally brought to an end in 2010 – with a whole life sentence. His first murder occurred in 1971, as he beat to death a love rival with an iron bar. After 26 years in prison, Wright rejoined society – but not for long.After taking advantage of a vulnerable woman, Wright again turned to murder. Wright forced his way into the home of the woman's son, in Bradford, brandishing a double-barrelled shotgun. The son was left critically injured in the attack, and his ex-partner killed in what police described as an execution.We hear from police officers on both investigations - and the surviving son - on how Wright committed his crimes and how he was brought to justice.Mark Martin became Nottingham's first serial killer – something he claimed he wanted to be – in 2005. Over a period of weeks, Martin attacked and killed three women whilst living rough in the city. We hear from police, and those who knew Mark Martin, to reveal how he took advantage of vulnerable people and believed he was untouchable.