Executive producer: Gene Roddenberry
Associate producers: Edward K. Milkis and Gregg Peters
Producer Fred Freiberger
Co-producer: Robert H. Justman
Story consultant: Arthur H. Singer

Story by: Jerry Sohl and Lee Erwin
Writer: Lee Erwin

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
Lieutenant Uhura: Nichelle Nichols
Garth of Izar: Steve Ihnat
Marta: Yvonne Craig
Donald Cory: Keye Luke

Stardate 5718.3

Elba II. The galaxy's insane people are treated on this planet and the Enterprise brings a new drug to cure them. Beaming down to hand over the drug Kirk and Spock meet the colony's governor Donald Cory - or so they think, but it is Garth of Izar, a former Starfleet Captain, who has developed the ability to change his appearance. Garth is insane and has taken over control of the colony. He plans to take over the Enterprise and dreams of being in command over a fleet.

He invites Kirk and Spock to a banquet and has Marta, an Orion woman, dancing for them. Spock says the dance reminds him about the dances taught to Vulcan children in nursery school, but he admits that children are not so well suited for it. When Spock openly counters to Garth's babbling of power and glory, the man becomes furious and orders him to be jailed.

Kirk is still treated as a guest. While he's resting, Marta enters his quarters and attacks him with a knife, but is stopped by Spock. This Spock talks a lot more and suggests Kirk what to order, he says he escaped his prison and managed to get weapons and seems eager to get back on board. Kirk calls Scott, who states a move of chess, clearly waiting for a concerted answer. Kirk hands over the communicator to Spock and says: "You give Scotty the code, if you are Spock." He is not.

Trying to intimidate Kirk Garth does not mind to kill Marta in a horrible way. He sends her outdoors in a not breathable atmosphere and while watching her struggling for air, through the window, triggers some device who blows up the woman. By now the real Spock has escaped his guards and suddenly faces two Kirks. They are fighting each other and Spock has to find out who's the real one. Each Kirk claims to be the true one and urges Spock to shoot the other, but Spock hesitates, until one of the Kirks shouts "Shoot both of us!" Spock shoots the other one who, when unconscious, turns into Garth. They free Cory and Garth is given the new drug hoping to cure him.