Yesterday's Son
A. C. Crispin
Book Description (jacket text):
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, 5,000 years ago, Spock knew a beautiful, primitive woman. Now he has gone back to meet his son!
Opinion:
This Star Trek novel is pretty good, joins in an intelligent way two TOS episodes and builds out of the facts a really new story. On the one hand the author uses the "guardian of forever" (mentioned in "The City on the Edge of Forever"), on the other there are some events described in
"All Our Yesterdays" which are continued (and outperformed). Although a very short book indeed neither the characters nor the plot suffer under that circumstance.
Only downer: without the background of both episodes it is close to impossible to have fun with the book although it is most unlikely that a non-fan would read a Star Trek novel.
"Yesterday's son" itself has a sequel; A.C. Cripsin continued the story in "Time for Yesterday" (not as well written as this one, though).