Erik and Ann Sheppard run a bar on a Greek island, but all is not what it seems: both have murky pasts that they would prefer to forget. Erik is a reformed alcoholic and Korean war veteran invalided out of the British army after a nervous breakdown. He left England after being controversially cleared of murdering a young girl. Ann, unknown to him, is a 'sleeping' agent, who had been instructed to marry him as a cover. Unfortunately, she has become genuinely attached to him, and trouble looms when her superiors decide to activate her for a mission. Their attempts to break her affections include sowing doubts in her mind as to whether Erik did in fact kill the girl in England. This dilemma is brought into sharp focus when another young girl is murdered, under very similar circumstances. Loyalties are tested to the very limit before the truth can be reached.