The Enterprise must protect the Guardian—or destroy it. But Spock has already used the portal to journey to the past. On the planet Sarpedion, 5,000 years ago Spock knew a beautiful, primitive woman. Now he has gone to meet his son!
But Zar is enmeshed in troubles of his own, and soon Kirk, Spock, and McCoy find themselves in a desperate struggle to save both their world—and his!