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 and a cut or break in the skin can literally cause death. After McCoy heals Parmen's wounds, Parmen and his fellow Platonians decide to use their immense telekinetic powers to force Kirk, McCoy and Spock to stay on the planet and behave as puppets for their amusement.

James Doohan (Lt. Cmdr. Montgomery Scott)
Michael Dunn (Alexander)
Liam Sullivan (Parmen)
Barbara Babcock (Philana)
Nichelle Nichols (Lt. Nyota Uhura)
Majel Barrett (Nurse Christine Chapel)
Ted Scott (Eraclitus)
Derek Partridge (Dionyd)

• This episode contains the first ever interracial kiss to be shown on American network television, between Kirk and Uhura (under Parmen's telekenetic influence). However, due to the camera angle, you can't see their lips touching.