Yesterday's Son

By A. C. Crispin

The Romulans attack the planet Gateway, where Federation scientists are studying the Guardian of Forever - the mysterious portal to the past.

The Enterprise must protect the Guardian - or destroy it. But Spock has already used the portal to journey to the past. On the planet Sarpeidon, 5000 years ago, Spock knew a beautiful, primitive woman. Now he has gone to meet his son!