Genre: Sci-fi/Star Trek
Read again? In another decade
The book starts off with a weak premise: Spock & Dr. McCoy are playing chess; a new girl comes over, asks Spock about Sarpeidon, the planet where Spock & McCoy went back 5,000 years in time (and Spock nailed Mariette Hartley--"All Our Yesterdays"). She's got pictures of some of the relics of Sarpeidon's lost civilization, including a recognizable Vulcan painted on one cave wall, where no Vulcan had gone before!
Here's the weak part: the Vulcan's so recognizable that Spock knows it's not himself--therefore it must be his son.
Of course he's going to use the Guardian of Forever to go back there. McCoy and Captain Kirk tag along. Poof! They go back and find Zar, now in his mid-twenties, living alone in the icy wilderness. He's a proficient hunter and survivor, but he's been lonely for years since his mother died. He willingly agrees to go back to the future!
This is a much better book than Diane Carey's Battlestations! and Dreadnought!; characterization is reasonably good, but the plot's very linear. There have to be Bad Guys, so Crispin brings in some Romulans who wonder why the Federation is spending so much time trying to keep the Guardian's planet a secret. Big fight, of course. Zar goes back to his own time--pretty much has to.