In May 1940, as the German invasion of the Netherlands is under way, the British government decides to send a team to the Netherlands on board to secure stocks of industrial diamonds before the invaders can get to them. Accordingly, two Dutch diamond experts, Jan Smit (Peter Finch) and Walter Keyser (Alexander Knox) with a British Army Intelligence officer, Major Dillon (Tony Britton), are dropped by ship off the Dutch coast. They survive a German air raid and escape the attention of a suspicious Dutch policeman. Needing a car, they manage to commandeer one driven by Anna (Eva Bartok), who is trying to commit suicide because she blames herself for the death of her Jewish fiance's parents. Anna turns out to be a member of the Dutch security forces and agrees to help the mission.