The Enterprise investigates a planet visited 100 years ago by the U.S.S. Horizon. Kirk, Spock, and McCoy beam down and find themselves in a culture similar to Earth gangs of 1920 Chicago. They are quickly taken prisoner by men in the employ of a mob boss named Bela Oxmyx, who wishes them to give him phasers in exchange for “a piece of the action.“ When they refuse, Oxmyx puts them under guard. Kirk creates a diversion with a card game called “fizzbin,“ but without their equipment, the trio must find a way to unite the planet and escape to the Enterprise alive.