The disappearance of a scientific team lures the U.S.S. Enterprise to investigate near Lactra VII. The starship U.S.S. Ariel is located there, abandoned, with its captain having transported to the planet's surface.

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

Majel Barrett (Lt. Randi Bryce)
James Doohan (Lt. Cmdr. Montgomery Scott)

• Though credited, George Takei and Nichelle Nichols do not voice any characters in this episode.
  
• James Doohan also voices Ariel commander Lt. Cmdr. Tom Markel.
  
• The Lactrans view the humans as lower level lifeforms and have placed them into a zoo.