Set in May 1940 this tense World War II spy thriller is set against the impending invasion of Holland by the Nazi's. In London, Jan Smit (Peter Finch) is in exile whilst his father, an eminent diamond merchant, remains in Amsterdam. Together with his countryman, Walter Keyser (Alexander Knox) Smit is persuaded to return to his homeland under the command of British Agent Major Dillon (Tony Britton). Their mission is to recover the industrial diamond stocks from the traders in Amsterdam before they fall into the hands of the advancing Wehrmacht. Landing secretly on the Dutch coast, our heroes are greeted with the chaos of locals fleeing the threat of the German invaders, and narrowly avoid disaster from a failed suicide attempt by the beautiful Anna (Eva Bartok). Anna is persuaded to drive the group through the deserted streets of Amsterdam where Smit attempts, with his fathers help, to persuade the diamond merchants to part with their stocks. His problem, the diamond merchants many of them Jewish, will be left behind to face the wrath of the Germans whilst their stocks have returned to London. Faced with a race against time Smit, Dillon and Keyser must recover what diamonds they can, dodge the fifth columnists roaming the streets, and make their rendez-vous on board ship in order to return to London... or suffer the consequences.