Let's Get Laid (1978)

A demobbed soldier, Gordon Laid, returning from World War II meets Maxine Lupercal, a member of a traveling troupe of actors returning to England on the same ship. As Gordon closely resembles a member of the troupe of actors, mistaken identity causes him to become embroiled in various murders and an international espionage plot involving a cigarette lighter that strangely affects electricity. The action reaches its comical climax on stage with Gordon and his double as the spies and the police converge on the theatre is a desperate attempt to retrieve the missing cigarette lighter.

Comedy