When two Chicago musicians, Joe and Jerry, witness the the St. Valentine's Day massacre, they want to get out of town and get away from the gangster responsible, Spats Colombo. They're desperate to get a gig out of town but the only job they know of is in an all-girl band heading to Florida. They show up at the train station as Josephine and Daphne, the replacement saxophone and bass players. They certainly enjoy being around the girls, especially Sugar Kane Kowalczyk who sings and plays the ukulele. Joe in particular sets out to woo her while Jerry/Daphne is wooed by a millionaire, Osgood Fielding III. Mayhem ensues as the two men try to keep their true identities hidden and Spats Colombo and his crew show up for a meeting with several other crime lords.
Karen Tandy enters a San Franisco hospital suffering from a tumor growing in her neck. Her surprised doctors think it's a living creature, a fetus being born inside the tumor. Fortune-teller Harry Erskine dismisses it – until one of his customers begins speaking in tongues and fatally throws herself down a flight of stairs, and Karen's surgeon attempts to cut off his own hand rather than excise her tumor. Erskine finally seeks help from another fortune teller, Amelia Crusoe, and her husband, to try to learn the cause of these supernatural events. When Karen's tumor gets larger, Dr. Snow speculates that within her tumor lives vengeful 400-year-old Indian spirit.
J.J. Hunsceker (Burt Lancaster), is a tyrannical Broadway columnist for the New York Globe who rules his demimonde with the press's power to create or destroy. Sidney Falco (Tony Curtis), is the hustling publicist who is consumed by desperate ambition and hates himself because of it; he will do anything to gain the admiration of Hunsceker ("My experience, in brief, is dog eat dog.") The film was shot in black and white by James Wong Howe, giving it a grittiness that underscores the class ranking among the characters. In the script by Clifford Odets and Ernest Lehman, Falco's early prediction - "Every dog has its day" - comes crashingly true.
While hiding from the royal authorities, Jacomo Casanova, the famous romancer, encounters his look-alike: Jacomino, a fugitive petty con man. Meanwhile, the Arabian Caliph and his wife are arriving in Venice for a state visit, and she insists on a night with the legendary lover. Through a series of erotic encounters and mistaken-identity comedies, Jacomo and Jacomino make their way back to Venice for their appointment with the Caliph's wife.