Concluding the series in which Angus Deayton investigates the art of deception.

This week's programme looks at liars with a mission. Whether it's saving a marriage or changing the world, the individuals in tonight's episode lie because the ends justify the means.
Angus Deayton introduces four very different people who feel they have right on their side, including a woman who acted as a spy and lived a double life of espionage with her husband and an undercover investigator who justifies his secret filming techniques to expose crimes.