Back of Beyond by C.J. Box

Cop Cody Hoyt has begun to put his life back together after many years as an alcoholic. When his sponsor, Hank Winters, is found dead in his cabin, Cody finds evidence that it's murder, not suicide. After being suspended from work, he conducts a rogue investigation with his co-worker, Larry, and is stunned to discover than the murderer is probably on the same excursion through Yellowstone that his teenage son, Justin, is on. Determined to rescue Justin and avenge a good friend's death, Cody will not stop until apprehends the killer. Meanwhile, fourteen-year-old Gracie is on the Yellowstone trip with her divorced father and older sister and she feels apprehension about the people with her. Who among them is evil? Back of Beyond is the third standalone thriller by C.J. Box. With the main characters of Cody and Gracie, the descriptive Montana/Wyoming setting and non-stop action, Box has written a real winner.