I can't say enough good things about this book. It's a well-crafted mystery/thriller with good characters, a spectacular setting, and a keep-you-guessing plot. I'd read one other C. J. Box novel before this (the Edgar-winning Blue Heaven); when I reached the end of this one, I put his remaining 16 novels on my to-be-read list.
The opening sentence is a grabber: "The night before Cody Hoyt shot the county coroner, he was driving without a purpose in his county Ford Expedition as he often did these days."
Cody is the main protagonist, and he's kind of a mess. He's a county cop, and divorced alcoholic; you get the impression that he's barely holding onto both his job and his sobriety. It doesn't help that when he's called out to investigate a fire at a remote cabin, he already knows the burned-up victim: it's Hank, his Alcoholics Anonymous sponsor, whose corpse is found next to an open bottle of Wild Turkey.
Everyone is convinced that the victim perished in a drunken wood stove accident. Cody knows it's homicide, although he can't convince his superiors of that. A computer's browsing history shows that Hank—or someone—recently checked out a wilderness trip into a remote spot in Yellowstone National Park. And (in a Dickensian coincidence) it happens to be a wilderness trip that Cody's son is being taken on by his ex-wife's fiancee.
We're then introduced to a second protagonist, 14-year-old Gracie Sullivan, who's on the trip with her slutty older sister, wimpy dad, and her wimpy dad's surprise new girlfriend.
It soon becomes apparent that a lot of characters have hidden motives and plans of their own. (Including the sleazy outfitter leading the trip and his employee/girlfriend.) Soon, folks start vanishing mysteriously from the trip. Back in Montana, Cody sets out in a desperate attempt to catch up with the group and save his son, but shadowy forces keep delaying him.
It's insanely readable. (I'd say it's a page-turner, but I read it on my Kindle. So it's a button-pusher.) Highly recommended.