Jewel thief Jack Rhodes, a.k.a. "Jack of Diamonds", is masterminding a heist of $30 million worth of uncut Gemstone. He also has his eye on lovely Gillian Bromley, who becomes a part of the gang he is forming to pull off the daring robbery. However, Chief Inspector Cyril Willis from Scotland Yard is blackmailing Gillian, threatening her with prosecution on another theft if she doesn't cooperate in helping him bag the elusive Rhodes, the last jewel in his crown before the Chief Inspector formally retires from duty.