This particular Star Trek novel is obviously a case of a self-indulgent fan-turned-amateur-author (presumably one of the first generation of Trekkies during and after the original series) using a Star Trek novel to publicly display her sexual fantasies about Spock, and must be understood in that context. As such, it's obnoxious and irritating, and I regret reading it (having had no idea). Doctor Who novels did the same thing at least once: in Kate Orman's Unnatural History, the Eighth Doctor's companion Sam attempts to seduce him (which, regrettably, was later duplicated on television with Amy Pond and the Eleventh Doctor).
What happens is basically that the Enterprise takes on a very attractive mission specialist who irrationally hates Vulcans for no obvious reason (McCoy eventually discovers that it's a psychological reaction to her Vulcan husband dying); she and Spock become trapped on a planet populated by hostile giant ants, and while defending themselves alone, mate (thereby positing that Vulcan mating is not restricted to the pon farr cycle).
Although I disdain this book for the above reason, I did find a character naming her cat "Fuzzybutt" highly amusing.