This is the story of Martin McGartland who worked undercover as a British agent inside the Provisional IRA. Captured by the Provos, he escaped and re-settled on the mainland, but later discovered that he had been deliberately sacrificed by MI5. During his years in hiding he was arrested and taken to court many times. Eventually the Crown Prosecution Service, advised by MI5, ordered his trial for attempting to pervert the course of justice. The jury found him not guilty, but the court gave his name and new identity away. McGartland travelled back to Belfast to try and discover why MI5 had attempted to organise his execution.