AllMovie

This episode finds Captain Kirk, Dr. McCoy and Mr. Spock exploring the planet Sarpeidon, whose sun is about to go nova. They discover cities and other components of an advanced civilization, but no inhabitants save one, a mysterious man (Ian Wolfe) who identifies himself as the "librarian." They learn that the "library" is a time portal, and that the inhabitants have escaped the doom of their world by taking new lives in past eras. Kirk accidentally steps through the portal and becomes trapped in this world's equivalent of the 17th century, and accused of witchcraft; Spock and McCoy, in turn, are stranded in the planet's brutal ice age, where they meet Zarabeth (Mariette Hartley), an unwilling prisoner of that era. Kirk must try to avoid execution, while Spock -- quickly reverting to his primordial Vulcan nature, brutal and lustful, as a result of moving into the past -- finds his growing love for Zarabeth interfering with his efforts at escape. And that escape becomes even more imperative when they learn that because of the particular way they were transported, they can only survive for a matter of hours.