The series starts with former members of the service explaining how they rationalise killing as part of their duties and what happens to that sharply honed killer instinct when they leave the service and return to civilian life.

Former SAS operative Colin Maclachlan recounts the events that led to a routine mission to Iraq going dangerously wrong when his cover was blown, leading to an intense period of captivity punctuated by mock executions and mob violence.

The series looks at the lasting legacy life in the service has on the men. Former SAS-member Yorky recalls the extreme hardships of a six-week mission inside Iraq and how the killing of a young Iraqi solider stayed with him for years.

The series concludes with a retelling of the eight-man patrol Bravo Two Zero's mission behind enemy lines during the First Gulf War in January 1991. A young goat herder exposed their position and they were hunted by the Iraqi military.