Aging rapidly after a planetary visit, the senior officers cannot be trusted with the ship.
After a visit to the planet Gamma Hydra IV, Kirk, Spock, McCoy and others begin to age rapidly, while Chekov, apparently immune, stays young. As the senior officers lose their memory and judgement, Commodore Stocker takes command and leads the ship toward the Romulan Neutral Zone.
The episode is notable for the makeup work and for showing the senior crew as frail. It also features a courtroom sequence in which Kirk's competence is questioned. McCoy races to find a cure, and Kirk uses a clever bluff against a Romulan ship to rescue the situation.