Director: James Goldstone
Writer: Robert Bloch

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols

Dr. Simon van Gelder: Morgan Woodward
Dr. Tristan Adams: James Gregory
Dr. Helen Noel: Marianna Hill
Lethe: Susanne Wasson
Ensign Berkley: Larry Anthony

Stardate 2715.1

  An escapee from the Penal Colony on Tantalus makes it onto the Enterprise inside a container and claims to be Dr. Simon van Gelder, part of the psychiatric staff. Though he seems to be mentally disturbed Dr. McCoy and Spock believe him. Kirk and Dr. Helen Noel, the Enterprise's psychiatrist, beam down to investigate. They discover that the Colony director, Dr. Tristan Adams, has altered a machine misusing it now to control people's minds, as a neural neutralizer. 

After Kirk found out he is the next who has to try it out. He is made to fall in love with Dr. Noel. Both are kept in the colony. On board Spock conducts a mind-melt with Dr. Gelder and finds out about Dr. Adam's actions. The planet though is shielded so that beaming down is impossible, unless the shields are lowered by the Penal Colony's staff – or by Dr. Noel who climbs through the air ventilation system and manages to cut off the power system for a moment. Enough for Spock to beam down with a team. By now Kirk has overpowered Dr. Adams who underestimated Kirk's strength. After the struggle Dr. Adam is by accident trapped in his own machine and suffers from it's effects for a long time until he is found. After having recovered Dr. Gelder takes over again the lead of the Colony.