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 HMS Walpole (D41) to secure stocks of industrial diamonds before the invaders can get to them. Accordingly, two Netherlands 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. Dodging German bombs and suspicious Dutch police and soldiers, they commandeer a car driven by Anna (Eva Bartok), whom they have just saved from trying to commit suicide. The four of them drive to Amsterdam.