When the U.S.S. Enterprise receives a distress call from the planet Platonius, Kirk, Spock and McCoy beam down to the planet's surface. There they find the planet's leader, Parmen, with a badly infected leg. The Platonians, while powerful psycho kinetics, have no resistance against physical injury. As Parmen's wife tells them, a cut or break in the skin can literally cause death. The only resident of Platonius that doesn't have "the power" is Alexander, a dwarf, who is everyone's jester and slave.
When Parmen's wound has healed and the landing party prepares to leave, they find the U.S.S. Enterprise's controls are frozen. Parmen has decided that it would be beneficial for them to have a resident doctor and tries to convince McCoy to remain. When he refuses, Parmen and the others try to convince him by subjecting Kirk and Spock to several humiliating scenarios. Still the doctor refuses and the three officers are locked away to ponder their plight.
After questioning Alexander, McCoy determines that the Platonians probably got their mental powers from eating the local foods. Something about Alexander's metabolism has kept him from acquiring those powers as well. McCoy prepares concentrated doses of kironide, the substance in the local food, and injects it into Kirk and Spock. Alexander, given the chance, refuses an injection. He doesn't want the same powers that his masters have.
As they discuss their next move, the shimmering of a transporter beam appear in the room and Lieutenant Uhura and Nurse Chapel appear. Without a word, they are jerked out of the room, as if controlled with invisible strings, and disappear. Kirk comments grimly that the men were apparently not entertaining enough for the Platonians.
Later, Uhura and Christine join the other officers, dressed in sparkling gowns and lavish makeup. Christine's is even vaguely Vulcan with slanted eyebrows and partially covered ears. What follows is a series of "games" designed to humiliate the U.S.S. Enterprise crew members and entertain the Platonians. McCoy, seated in a place of honor beside Parmen, is expected to accept the leaders offer to stay and serve as their physician.
Kirk and Spock are forced to fight each other and Spock is made to sing "Maiden Wine" to the two women. Finally, Spock is paired on a loveseat with Christine, while Kirk shares one with Uhura. They are forced to make advances on the women. The play gets nasty then, as Kirk and Spock take up whips, which they snap at their respective partners. By now, however, the doses of kironide are beginning to take effect and both officers now resist the Platonians powers and throw down their weapons.
Kirk tells Parmen that they can recreate this power whenever they want and if the Federation finds that Parmen and his people have fallen back to their old ways, there will be trouble. With this, Kirk calls for the U.S.S. Enterprise to beam them aboard ... along with Alexander, who will be coming with them to start a new life.