The powerful, long-awaited sequel to Yesterday's Son. Waves of distorted time are crashing through the universe - destroying everything in their path. Federation scientists pinpoint the source: the Guardian of Forever, the portal to the past where Spock had once journeyed back to meet his son, Zar. Only Spock's son has ever made mind contact with the Guardian - and now Spock, Kirk, and McCoy are reunited on a desperate mission to take the Enterprise to Gateway. Their goal is to bring Zar out of the past to contact the Guardian of Forever and save civilization. But Zar is leading his primitive people into a calamitous war - and unless Kirk and Spock can change the course of history, Zar is doomed to die!
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