When a retired thief, the Ace of Diamonds (Joseph Cotten), warns his protégé to quit while he's ahead, Jeffrey Hill (George Hamilton) ignores the advice and steals all the jewelry he can. Bumping into Olga Vodkine (Marie Laforet) on a luxury cruise while trying to rob the same stateroom, Jeffrey agrees to team up with her and pinch the fabulous Zaharoff diamonds. Although the gems are locked in an impenetrable bank vault in Paris, Jeffrey and Olga embark on an impossible heist that could land them in riches or in prison.