• Production Code: 60
• Stardate: 5029.5
• Original Air Date: Oct 11, 1968
• Writer: Edward J. Lakso
• Director: Marvin Chomsky
• Guest Stars:
  • Craig Hundley (Tommy Starnes)
  • James Wellman (Professor Starnes)
  • Melvin Belli (Gorgan)
  • Majel Barrett (Nurse Chapel)
  • Pamelyn Ferdin (Mary)
  • Caesar Belli (Steve)
  • Mark Robert Brown (Don)
  • Brian Tochi (Ray)
  • Lou Elias (1st Technician)

Kirk and the crew, visiting a scientific colony manned by several human families, are shocked to find that all but the children have died violently - and the children do not seem to care about anything but playing. Aboard the Enterprise, the children gradually begin to influence and take over the minds of the crew as part of a plan by their "friendly angel," a seemingly benevolent alien called Gorgon who uses children as a means of spreading his influence, and unless he can find some way to expose Gorgon's true intentions, Kirk will become a prisoner on his own ship.