The U.S.S. Enterprise tracks a mysterious SOS to an ancient planet presumed long dead. The crew hears a voice from a telepathic being named Sargon, who asks Kirk to beam down to the surface. The landing party find themselves in a vault, where they encounter a glowing sphere that identifies itself as Sargon, who explains that his people were destroyed in a cataclysmic war half a million years ago, and now exists only as pure thought. Sargon and two others of his kind need to "borrow" the bodies of the Enterprise officers long enough to construct new artificial ones.

Diana Muldaur (Dr. Anne Mulhall)
James Doohan (Lt. Cmdr. Montgomery Scott)
Nichelle Nichols (Lt. Uhura)
George Takei (Lt. Sulu)
Cindy Lou (Nurse)
Majel Barrett (Nurse Christine Chapel)

• Diana Muldaur will go on to play Dr. Pulaski in Star Trek: The Next Generation's second season, beginning with "The Child".