The U.S.S. Enterprise answers an old distress signal to find an unnamed planet that is almost an exact duplicate of Earth in the 1960s. A landing party beams down and discovers that 300 years before, the natives of the planet conducted experiments to prolong life, but had instead created a deadly virus, which killed all adults by rapid aging and madness. In children, the virus slowed the natural aging process greatly, leaving them in a state of prepubescence for centuries.

Kim Darby (Miri)
Michael J. Pollard (Jahn)
DeForest Kelley (Dr. Leonard H. McCoy)
Grace Lee Whitney (Yeoman Janice Rand)
Keith Taylor (Jahn's Friend)
Ed McCready (Boy Creature)
Kellie Flanagan (Blonde Girl)
Steven McEveety (Redheaded Boy)
David Ross (Lt. Galloway)
Jim Goodwin (Lt. John Farrell)
John Megna (Little Boy)