The U.S.S. Enterprise is bringing a new medicine to the mental hospital on Elba II with which they hope to eliminate mental illness forever. When Kirk and Spock beam down to the facility of 15 inmates, they find that the asylum has been taken over by Garth of Izar, who was once a famous starship captain. Garth convinces them that he is the head of the facility, in an attempt to gain control of the U.S.S. Enterprise and conquer the galaxy.

James Doohan (Lt. Cmdr. Montgomery Scott)
Steve Ihnat (Garth of Izar)
Yvonne Craig (Marta)
George Takei (Lt. Hikaru Sulu)
Nichelle Nichols (Lt. Uhura)
Richard Geary (Andorian)
Gary Downey (Tellarite)
Keye Luke (Gov. Donald Cory)