Release Message:  When Kirk, Spock (Leonard Nimoy), and McCoy investigate the disappearance of a doomed planet's population, they find themselves trapped in different periods of that world's past.

Description:  When Kirk, Spock, and McCoy investigate the disappearance of a doomed planet's population, they find themselves trapped in different periods of that world's past. Wikipedia: The crew of the Enterprise are trapped inside a time portal on a world threatened by a supernova.