Jeff Hill, a master thief known as the Jack of Diamonds, skillfully uses his acrobatic ability and cleverness to perform a series of jewel heists that target glamorous film stars such as
Zsa Zsa Gabor,
Carroll Baker and
Lilli Palmer. While executing a heist on a luxury liner, Jeff encounters and wrestles with an unknown competitor in the dark who is attempting to steal the jewels that Jeff is pursuing. Jeff
abseils down the side of the ship to a waiting boat, and his rival soon follows, a beautiful woman named Olga who boards her own escape boat. Jeff visits with his mentor, the Ace of Diamonds, who advises him to quit while he is ahead. Jeff meets Olga, at first not realizing that it was she with whom he fought aboard the ship, and she introduces him to her father Nicolai, an old friend of the Ace of Diamonds. Nicolai persuades Jeff to team with Olga to rob a heavily guarded vault containing a priceless diamond necklace. Jeff first surreptitiously enters the police station to access the code for the vault door. Nicolai, Olga, Jeff and the Ace plan the robbery meticulously, studying accurate models of the building and outlining the actual dimensions of the guarded area with tape on the floor of Jeff's mansion. On the night of the heist, Jeff gains access to the vault despite the presence of many police officers nearby. He swaps the jewel necklace for an exact copy but just as he is about to leave the vault, he inadvertently trips an alarm. The police spring into action and pursue Jeff and Olga, but Ace emerges at the top of the building intentionally in full view of the police searchlights so that he may be captured while Jeff and Olga slip away in the darkness with the jewels still safely stashed. Jeff approaches
Interpol inspector Wilhelm Von Schenk with a proposition to free Ace and avoid prison time for himself. He reveals that he has replaced many of the world's most famous jewels with identical copies, and the victims are not even aware that they now possess fakes. He offers to secretly return all of the stolen jewels and end his career as a thief if Von Schenk, who wishes to avoid the repercussions that will ensue if the fakes are discovered, will allow Jeff and the Ace to go free. The stolen jewels are secretly restored with the same cunning techniques used to steal them. Jeff, now penniless, must leave his spacious mansion and his glamourous life as an international thief. However, Nicolai reveals that he has withheld one genuine diamond that he presents as a gift for Jeff and Olga. ==Cast==