The U.S.S. Enterprise finds a crewless starship, the U.S.S. Exeter, in orbit around the planet Omega IV. The boarding party from the U.S.S. Enterprise contracts a virus that may have killed the Exeter's crew, but the biosphere on Omega IV is found to contain an immunity and the party is beamed to the surface. There they discover Captain Tracey, the commander of the U.S.S. Exeter, who has been violating the Federation's Prime Directive by interfering in the politics of the natives, using his phaser to protect the asian-like villagers, the Kohms, against the barbarian raiders, the Yangs.

Morgan Woodward (Captain Ronald Tracey)
Roy Jenson (Cloud William)
George Takei (Lt. Hikaru Sulu)
Nichelle Nichols (Lt. Uhura)
Irene Kelly (Sirah)
Morgan Farley (Yang Scholar)
David L. Ross (Lt. Galloway)
Lloyd Kino (Wu)
Ed McCready (Dr. Carter)
Frank Atienza (Executioner)

• Captain Ronald Tracey was commanding officer of the U.S.S. Exeter NCC-1672.
  
• Yet another planet with a society based on an Earth historical period.