It is February 1929 in the city of Chicago. Joe (Tony Curtis) is a jazz saxophone player, irresponsible gambler and ladies' man; his friend Jerry (Jack Lemmon) is a sensible jazz double-bass player. Together they accidentally witness the Saint Valentine's Day Massacre. When the gangsters, led by "Spats" Colombo (George Raft), spot them, the two have to run for their lives.