The Enterprise crew is taken captive by a race of primitives on newly discovered planet Delta Theta III.

William Shatner (Captain James T. Kirk)
Leonard Nimoy (Commander Spock)
DeForest Kelley (Dr. Leonard H. McCoy)

George Takei (Lt. Hikaru Sulu)
Nichelle Nichols (Lt. Uhura)
Majel Barrett (Nurse Christine Chapel)
James Doohan (Lt. Cmdr. Montgomery Scott)

• Commander Ari bn Bem was assigned to the Enterprise as an independent observer. He is Pandronian, a "colony creature" where each individual is made up of multiple organisms.
  
• Kirk gives his full name as "James Tiberius Kirk" for the first time in this episode.
  
• Bem was voiced by James Doohan.
  
• Nichelle Nichols voices the Alien God, who calls the native Delta Thetans her "children," and eventually allows Spock and Kirk to leave if they promise to never return, allowing the natives to evolve and develop naturally.
  
• Dr. McCoy does not appear in this episode.