Mr Pidgeon is the unlikely and lucky owner of a large yacht and a desert island. Gentleman sleuth Roger Sheringham is one of the members of the party Pidgeon invites for a cruise. When the ship and its crew return to port without them, the party are marooned for a fortnight on the private island. Sheringham is shocked to discover Pidgeon has organised the whole thing as an experiment. He has brought them together to enact a bizarre murder and detection game. But then the madness starts and tragedy strikes...