Romantic comedy which has Barney Lincoln and Angel McGinnis as a pair of amorous adventurers in the gambling places of London and the Riviera. Barney Lincoln is a rambling gambling man who scores sensational wins at poker and chemin de fer because he has succeeded in marking the original plates for the backs of all the playing cards manufactured in a plant in Geneva and used in all the gambling joints in Europe. In his gambling depredation, Barney is spotted by Angel McGinnis, the daughter of a Scotland Yard Inspector 'Manny' McGinnis on the lookout for a man to do a job. The inspector enlists Barney's help in playing poker with a shady London character whom Scotland Yard wants to force to financial ruin.
Despite being independently wealthy, American Barney Lincoln, just because he can, devises and executes a plot to mark the master printing plates for the playing cards manufactured by Geneva-based Kaleidoscope, whose cards have an intricate kaleidoscope pattern on their backs. In marking the cards and knowing to which casinos the cards are to be shipped, Barney is able to win big at casino card games by reading the marked cards. Along for the ride is his new London based girlfriend, Angel McGinnis, who unknown to Barney has her own motivations in following him. Angel doesn't know what Barney is up to beyond believing that he is a good card player - too good. However, Scotland Yard does know what Barney is up to, and they co-opt him for a ploy of their own, namely to squeeze one of their marks, sadistic global narcotics dealer Harry Dominion. Dominion, who is currently deep in debt to finance a project, owns and operates his own casino, and Scotland Yard wants Barney to drain him of his funds at this vulnerable state in his life through card games of chance at his casino. Barney has no option but to cooperate with Scotland Yard. In doing so, Barney puts his and Angel's lives at risk especially if Dominion figures out Barney's scam.
- Barney Lincoln (Warren Beatty) is a cheeky young playboy with a taste for gambling who devises the ultimate scheme to cheat the casinos. After finding out that all of the casinos use the same playing card manufacturer, he breaks in and marks the kaleidoscopic pattern on printing plates for the cards. Soon the winnings mount up as he travels across Europe beating the odds. But Barneys troubles begin when he falls for the swinging fashion designer Angel (Susannah York), who discovers his deception. Her father, Manny McGinnis (Clive Revill), is a Scotland Yard inspector who offers Barney a deal. He will keep quiet about the cards if Barney helps him catch international drug smuggler Harry Dominion (Eric Porter) through a high-stakes poker game