Great Britain, 1944, during World War II. Relentlessly pursued by several MI5 agents, Henry Faber the Needle, a ruthless German spy in possession of vital information about D-Day, takes refuge on Storm Island, an inhospitable, sparsely inhabited island off the coast of northern Scotland.

In order to enjoy a romantic private swim together, Jo and Eddie hide when their local swimming pool is closing for the evening. But unknown to them, a killer is on the loose - and in the building with them.