Early “Earl” Coffin flies into Great Falls, Montana, on business. He works for a Seattle firm that brokers collectibles, and he has a rare revolver to authenticate. The gun is rumored to be the one used in a 1957 bank robbery. He also promised his Aunt Carla he would look in on her son, his cousin Robby. It should take an hour.

Robby’s phone call is odd. He is scared of someone and wants Earl to sit in his kitchen “for insurance.” Earl drives out to Alkali Road anyway. On the way, a pickup nearly runs him off the gravel. At the end of the road he finds the trailer empty and the door hanging open. Then a hard-edged young woman named Donna kicks her way in, and the two of them find Robby’s body in the bathroom.

Both of them have reasons not to talk to the cops. So Coffin starts asking questions himself, and he finds that everyone in Ulm and Great Falls seems to have known Robby a little too well. There are the used-car lot where Robby worked, a cast of card-playing neighbors, and a couple who claim the antique gun was stolen from their bedroom. There is a quiet Montana past that doesn’t want to stay buried. When a second death follows, Coffin realizes that a decades-old crime and a fresh one may share the same weapon.

Meanwhile his boss Sammy drags him into a side hustle involving a mysterious painting. It might be worth a fortune, or it might get them killed.

Murder on Alkali Road is a traditional whodunit with dark humor. It has a wry, breath-counting hero, a big-sky setting and a plot of double-crosses and hidden motives. It should appeal to readers of Craig Johnson, C.J. Box and Tony Hillerman.