Ep 4. A Piece of the Action

Captain Kirk, Mr. Spock, and Dr. McCoy beam down to an unexplored planet to investigate the fate of a lost Starfleet ship, the Horizon. To their surprise, they discover that the planet is highly civilized, resembling 1920s Chicago with prohibition-era gangsters and Tommy guns. The inhabitants are descendants of the Horizon's crew who, having received a book on Chicago gangsters as their only vestige of Earth culture, have organized themselves into a group of thugs emulating the gangsters of old.

Kirk is taken captive by one of the warring factions and is forced to use his street smarts to win the trust of the gang leader, Boss Oxmyx. Meanwhile, Spock is kidnapped by another gang, the Krako, and is challenged to a fight to the death in their arena. With the help of Kirk and McCoy, Spock escapes and the trio works to convince the warring factions to unite and progress beyond their imitation of Earth's gangster culture.

As they try to leave the planet, the crew realizes that the Horizon's book has had a lasting impact on the world and they leave behind a copy of the Federation's database to hopefully guide the planet towards a more peaceful and civilized future.