This is one of the best Star Trek novels I have read. That could be just because I like Spock. ;-) It is a sequel to "Yesterday's Son" which was Crispin's first published book, I think. I borrowed that one from the library and since they didn't have this sequel, I got it from PBS.
One of the better Trek novels, centering around a malfunction in the Guardian of Forever which is wreaking havoc in the universe. Crispin's strength is her deep affection for and understanding of the characters as they age and change through the established TOS timeline.. She returns here to a pocket universe she created earlier, in which Spock's brief relationship with a woman caught in a doomed planet's ice age resulted in a son. The son is now an adult, and embattled in his own time, when Spock, Kirk, and McCoy travel through the Guardian to seek his help.
