During World War I, a German officer infiltrates the British naval base at Scapa Flow, not realising that his contact has been discovered and replaced by a British agent. Although they seem attracted to each other, Hardt remains committed to his sabotage mission, and ?Joan' to ensuring it fails.
Conrad Veidt (Capt. Ernst Hardt), Sebastian Shaw (Cdr. Davis Blacklock), Valerie Hobson (Joan), Marius Goring (Lt. Schuster), June Duprez (Anne Burnett)