The detention of Kirk, Spock and McCoy in 2268 by the Platonians, a small society of long-lived psychokinetics who wanted to keep McCoy as their physician.
The Platonians were refugees from a dead star system who had lived on Earth in the age of Plato and modelled their society on his ideals. Thirty-eight of them survived on Platonius under their philosopher-king Parmen, wielding psychokinetic powers but with almost no resistance to infection.
In the Original Series episode Plato's Stepchildren the Enterprise answers their call for medical help. McCoy cures Parmen of a wound, and the Platonians then refuse to let him go. They torment Kirk and Spock for sport, force Spock to laugh and weep, and bring down Uhura and Chapel to take part in their entertainments.
McCoy traces the power to kironide in the local food and gives Kirk a concentrated dose. Kirk overpowers Parmen and departs with the mistreated jester Alexander.