The movie was good, so I'll third
The Friends of Eddie Coyle.
I'd also like to nominate
Holmes On the Range by Steve Hockensmith.
Goodreads
From Booklist
Spoiler:
*Starred Review* The Amlingmeyer brothers--Big Red, our narrator, and Old Red--grabbed a job at the mysterious Bar-VR Ranch to avoid a winter without food or money. One of the hands at the ranch is found with a bullet in his brain and another ends up seemingly trampled, but no one can recall a stampede. The shadowy miscreants had best watch their backs, however, as the Amlingmeyers are not your ordinary cowpokes. Old Red can't read but has been entertained trailside by Big Red's reading Sherlock Holmes stories from Harper's Weekly. Old Red thus considers himself a budding master of what he calls "deducifyin'." With Old Red as a six-gun Holmes and Big Red as a skeptical, nervous Watson, the pair ferrets out the killers and motives from a colorful cast of characters with names such as Puddin-Foot, Tall John, and Swivel-Eye. The Amlingmeyers have graced the pages of Ellery Queen's Mystery Magazine, and their initial book-length case is every bit as memorable. At times, they may remind readers of Joe Lansdale's Hap Collins and Leonard Pine with their smart mouths, penchant for trouble, and unflagging loyalty to each other. This is a great reworking of the Holmes conceit, and one suspects Hockensmith will have a steady readership as long as the Amlingmeyers are on the case. Wes Lukowsky