There are some characters who haven't been seen before, or who weren't in Lonesome Dove, anyway, and they provide some amusement. One, Inish Scull, is Gus and Call's captain in the rangers at the start of the book. He's a weird, strange character, and frankly should have been dropped two thirds of the way through the book when he returns to New England, or alternatively reintroduced to the plot somehow. His wife is even more outrageous than he is, and somehow is so annoying you're almost hoping the Indians get her and inflict some of McMurtry's patented unpleasantness upon her.
That being said, there's not much of a plot here, and there are conflicts with other books (notably Lonesome Dove itself). There's also the issue of history, and historical detail. It's as if McMurtry doesn't care, or doesn't know, and his publisher is uninterested too. So one character sings a song before it was written, another has a gun that hasn't been invented yet. The Civil War is almost an afterthought to the story. Frankly, Gus and Call would have been a lot more interesting if they'd gone east to fight in the war (many Texas Rangers did) and wound up at Pea Ridge or something. *That* would have been interesting. Instead, they act like the war didn't happen, almost, and no one else pays it much attention either. The one Northern-born ranger stays with his troop and rangers on, without much mention of his dilemma.
I've enjoyed many of McMurtry's books, and I enjoyed the characters here, but the plot was very thin. I can only recommend this book to those who already know they enjoy McMurtry, and are aware of what they're getting into.