Peter Davison stars as gentleman sleuth Albert Campion, alongside Brian Glover as his manservant Magersfontein Lugg, in this feature-length adaption of Margery Allingham's classic mystery novel set in the 1930s. Aboard a luxury liner, Campion crosses paths with American Judge Lobbett who is fleeing to England with his children. Campion offers the family safety from a criminal gang headed by the elusive Simister at the Mystery Mile, a coastal retreat in Suffolk.