Oh boy...this book was...awful. Firstly, we've got a whole bunch of Klingon lore that is trying to build on previous novels...and ends up portraying the Klingons completely differently than they would later be developed - which is funny considering that TNG was in pre-production during this novel's publication. You think somebody, somewhere would be communicating this information to someone. But, on to the story.
A lady-scientist, and former Starfleet Officer, nearly dies in an earthquake on a world near the Federation-Klingon Empire border, and is subsequently rescued by Klingons. Specifically Kang. of TOS fame, who is also apparently next-in-line to be Emperor. You see, lady-scientist, Jean, has been developing a new strain of that magical Trouble With Tribbles wheat, and the Klingons want it desperately because the entire Empire is currently suffering a famine due to a blight, and magic wheat is the cure, but it's also super secret and no one can know about it. At any rate, Kang decides that the best way to handle his captive is by forcing himself on her - 'cause he's a real hero type. But it's okay, because Jean realizes that she secretly likes people who imprison her and try to rape her, so she starts banging him and then Kang decides he wants to make her his new Consort...although, she's still under the Klingon-version of the life debt, so even if she accepts his offer, which spoiler she does, she still can't consent seeing as how she has no freedom...but, I digress.
Eventually, Jean escapes back to the Federation and convinces both them and Kang that they need to negotiate in peace because the Federation will happily help them solve their famine issues, no questions asked, but, of course, Klingons are too proud to accept charity, so, blah, blah, blah, posturing and penis-measuring between Kirk and Kang. Oh, at one point, another Klingon, who coincidentally has sworn a life debt to Jean, accidentally wanders into a restricted area on the Enterprise, because, we later learn, Klingon's don't see all of the visible spectrum, a.k.a. they can't see red, but they can see two colors into the ultraviolet range that we can't - tuck that lore away in the "will never be talked about again" category. But, Security stops him and then proceeds to torture him with fists to the face while questioning him until Spock tells everyone about the "no see red thing" and it's all been a misunderstanding...no hard feelings, right friend? Sorry we in the Federation, who have been trying to convince how fun and friendly and happy and not evil we are beat the shit out of you because you were walking around a place we didn't bother to put door locks on.
Oh, Jean also gets captured by some other Klingons too as she is escaping the Empire and is tortured to the point of death six times, they resuscitate her every time...but, it's okay, because Kang didn't know about it, and is sexy and she wants to bang him, even though he doesn't really punish the torturers, well, maybe a slap on the wrist. We just really need to understand Klingon culture, the book keeps telling us, to see how truly amazing and compassionate they are.
During the climax phase, at the negotiations, Kirk somehow accidentally and unknowingly combines all the words together that activated Jean, who turns out wasn't just a humble lady-scientist after all, but was actually a super-spy, Starfleet agent, who was planted into the Klingon Empire to convince them to negotiate with the Federation, because the Federation knew about the famine all along and wanted to help the Empire, but knew they wouldn't accept charity, so they sent Jean to contact a pro-Federation group in the Empire...and also to get raped, tortured, and killed...just like the peaceful, enlightened, humanitarians they are.
I swear...these TOS books are like the absolute worst. In an alternate history, where The Next Generation never existed, Star Trek would be one of the those best forgotten chapters in science fiction history...