Michael Pickup, a skilled but trouble-prone RAF pilot in the squadron which ferries agents and saboteurs in and out of Nazi occupied Europe, find himself despatched to neutral Sweden. He is to bring back two witnesses to the hideous crime that one day will be called the Holocaust. Fumbling his way through the wiles of opposing factions and secret services, consoled by a spirited daughter of a Swedish nobleman, he steels himself for a desperate flight into the heart of darkness.