The Cat Who Came for Christmas, by Cleveland Amory (pub. 1987)
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I'm not actually sure if I read this in the late 80s or the early 90s. In fact, I'm not 100% sure I did read it, but I think I did. It would have been a copy I borrowed from my grandmother, probably. There's a sequel, The Cat and the Curmudgeon, the title of which sticks out perhaps just a bit more in my memory. So I think I read both books, but the latter is the one I'm slightly more confident in saying that I read. However, I really don't remember anything about the plots of either book. But I probably enjoyed them, at the time. There's also a third book in the series, but I'm pretty sure I never read that. At any rate, I obtained a used copy of this book in late 2019, and after reading it, I still couldn't say for sure whether I'd read it before or not. But now I have.

Cleveland Amory was a writer and commentator on animal rights, who founded the Fund for Animals in 1967. But the book begins in 1978, on Christmas Eve, when he and a friend rescue a stray cat. He later decides to keep the cat (or be kept by the cat), who, after a great deal of deliberation on the subject, he names Polar Bear. The book takes place over the course of a year, ending on the following Christmas, in 1979. But the book is definitely not a Christmas story, despite the title. Most of the story is about Amory and Polar Bear getting used to living together and getting to know each other. Amory often talks to the cat, and treats his own assumptions about what the cat is thinking as if the cat was actually holding conversations (or debates, or negotiations) with him... though without really giving the cat lines of dialogue, or anything fantastical like that. It's a fairly short book, so it's not like it focuses on everything that happens throughout the year, just some of the major points in their relationship. But it dwells on each of those points at greater length than one might expect would be possible. And Amory's writing is always rather amusing. But the book also includes some segments about the activism of the Fund for Animals, which is also interesting.

And I'm not sure what else to say. It's about as simple a plot as you're likely to come across in any book that isn't written specifically for young children (though certainly this book can be appreciated by readers of all ages). And... I expect I'd like to read (or re-read) the sequels at some point.