This is actually the third Slocum book and you can tell this is from back when the paperback industry was in full swing, because this is kinda a real book. There's some strong prose in there. And the plot is at least a good-faith effort at a story.
After a cattle drive, Slocum gets in trouble over a woman (this is about the only cocksmanship we see, as even the titular Kate giving into his charms as rendered as one Fade To Black after another). The sheriff railroads him for getting into a fight and gives Slocum a choice between working on the ol' chain-gang and escorting the Widow Kate to Wichita. Naturally, Slocum takes the job, even if he hates escort missions as much as any gamer, and the rest of the book is basically the trouble they get in on the way to Wichita (they run into both Indians *and* Mexicans) and the obvious reveal at the end, which has Slocum take a surprising (and not too convincing) anti-crime stance after I've already read about him robbing trains.
Of course, those bad guys didn't bother to pull a Hollywood good guy robbery, where you take all the money without hurting anyone. Idiots, right?
Anyway, it leads to a bit of an anticlimax, like the writer is just padding things until he finally reaches his word count, but things do wrap up however belatedly and, uh, yeah, that's Slocum And The Widow Kate. Maybe I should only give this three stars, but heck, it's a nice day out, let's be sweet.