A remarkably Earthlike planet is the home of a human-like civilization whose entire adult population was wiped out by a virulent disease. The children remain, although their growth has been slowed down to the point that Miri - a teenage girl found by Kirk and a landing party - could easily by 300 years old. Miri develops a crush on Kirk, but at the same time reports back to a gang of unruly children who plot to kidnap the landing party, beginning with Yeoman Rand. Kirk, Rand and even Miri begin to show signs of the disease, which gives Kirk a chance to prove that the disease will eventually kill all of the children - but they are unwilling to admit they need help or the 'stuffy' advice of an adult.
