Executive Producer: Gene Roddenberry
Producers: Gene L. Coon + John Meredyth Lucas
Associate Producer: Robert H. Justman
Script Consultant: D. C. Fontana

Writer: Gene Roddenberry
Dir.: Vincent McEveety

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Captain Tracey: Morgan Woodward
Sirah: Irene Kelley
Wu: Lloyd Kino

  Omega IV. Reaching its orbit the Enterprise finds the U. S. S. Exeter orbiting the planet and no answer. Kirk, Spock and McCoy beam over and find all the people on board dead and covered by crystallized powder. They all were affected by a deadly virus. So are the Enterprise officers. Under these circumstances, the trio cannot go back on board and decide to search for a cure down at Omega IV. There, they meet captain Tracey, the captain of the Exeter. He is sure the planet atmosphere provides immortality in humans, because the natives are all very aged and healty and weren't affected by the infection he and his crew brought on the planet. Spock wonders how the natives know about phasers. 

Some of the people on the planet look like Asian Earthers and call themselves the Kohms. But there are others: The Yanks. First the Kohms lock in Spock and Kirk. In the cell Kirk has his first encounter with 2 Yanks- they fight. Finding a key close by, they can escape, after Spock neckpinches one of the Yanks and therefor intimidates the other. The Yanks are in war with the Kohms and take over the village where Tracey, Kirk, Spock and some Kohms live. All of a sudden the names appear familiar: Kohms for communists and Yanks for Yankees. Immortality suddenly gets close- these people have lived long since their contact with Federations ships still remembering the old rivalries. But it is a part of them and not applicable to the others. The prolonged stay on the planet and something in Omega IV's atmosphere has actually killed the virus the three have been suffered from. 

All the time Tracey behaves hostile towards Mr. Spock. Trying to save his skin, Tracey denounces Kirk and Spock, especially turning against Spock telling the Yanks that Spock is Satan. He triggers the Yanks into killing Spock. When the Yanks listen to his heart (not knowing the Vulcan heart is in the abdominal region) and do not find a sound, they are sure, Tracey is right. Just before killing Spock Kirk remembers one of their laws: The good wins over the evil. He suggests a fight ... him against captain Tracey. Spock now uses his Vulcan power over human women - hypnosis. Kirk wins over Tracey and the leader of the Yanks tells him to kill him, because it is written that the good must destroy the evil. Focusing on one of the ladies, Spock makes her bring the communicator and opening it- by this giving a signal to the ship. Immediately crew members beam down and rescue them. Captain Tracey is taken along – under arrest – for violating the Prime Directive.