
I just finished re-reading this novel as part of my re-readings of older novels from the 1980s. This book was published in 1983 and according to Memory Alpha, takes place in 2274. The book makes clear this is a post-TMP novel. After reading the M&C novels published by Bantam my expectations for this novel were pretty low. Overall it's marginally better than their earlier novels. But I still found it a bit of a slog to get through.
It features two competing factions that believe in a sort of collective consciousness will bring civilizations to a higher being, in this case the Totality and the Oneness. The Enterprise is sent to escort an Ambassador, Gailbraith, who belongs to the Oneness to a human colony who had left Earth during the wars of the 21st century to form a new collective but who have been subjugated by the Totality. They are supposedly the 'New Humans' that Gene Roddenberry touched on in his novelization of TMP. On the way they pick up a half Zaran named Thane who catches the attention of both Captain Kirk and Spock creating a love triangle. The problem is once Thane mates with another being they become permanently entangled (in some ways similar to TNG episode "The Perfect Mate), and Spock may die if he does not become one with her. They become embroiled in a final battle between the Totality and the Oneness and Kirk, Spock and Thane must find a way to defeat both. They manage to solicit Gailbraith's help and the implication is that while they succeed, one day the Oneness may come calling.
Like many M&C novels I have read, they do actually bring up some interesting concepts. Such as the whole collective consciousness idea and the "new humans." But they don't really develop it any further. The new humans are barely mentioned in the latter half of the book as it becomes a love triangle story more or less. Christopher would develop the 'new human' idea further in his Ex Machina continuity, in particular The Higher Frontier, though his novel takes it in a completely different direction. This novel, like so many M&C novels, seems to take great pleasure in making Kirk appear weakened and a shadow of himself while making Spock dominant. Unlike some earlier novels, however, this one doesn't really show any romantic or sexual overtones between the two. In this case they are essentially vying for the attention of the same woman.
Another complaint I had is this novel seems to abandon everything Spock had learned about himself by the end of TMP. He appears much more like the Spock that first arrived at the Enterprise in the film. An almost total lack of emotion and almost hostile stoicism towards the crew. While the novel was released after TWOK had come out, it appears likely M&C had written it prior to the film's release based on how the characters unfold. That film interestingly enough does a better job of developing Spock's newfound appreciation of his human half that he had discovered at the end of TMP (whether accidentally or not--that was one element that seemed a natural development between the two films). Triangle, however, does not. It puts Spock firmly back into his Kolinahr mentality. Of all the original series characters in the novel, only McCoy seems to be written with the right characterizations. His felt the most consistent with the TV series and TMP. The other characters, Scotty, Sulu, Chekov and Uhura, don't really have much to do here.
I'd rate it as 'fair.' It was better than the Phoenix novels, though that isn't saying a whole lot. There are some interesting elements that are brought up that if developed could have made this a better novel IMO. But they seem obsessed with this Spock dominating Kirk idea that it seems they can't get that out of their way. Sometimes it becomes downright annoying. Like again?

Next up for me will be the 6th novel, The Abode of Life by Lee Correy, his only novel. I've been trying to read the novels from the 1980s written in published order by the same author since it appeared back then many authors carried on ideas they had begun in their prior novels (sort of like a mini-continuity). After that I will re-read the 2 novels written by Gene DeWeese that he loosely based on this novel--my favorite Star Trek novel of all time Chain of Attack, then The Final Nexus.