In Malcolm Brooks’s first novel, it is 1956 or thereabouts. Elvis Presley is “this new singer,” and “Blackboard Jungle” is playing at the movie theater in Billings, Mont. But when Catherine Lemay asks the teenage Miriam, “Is rock and roll here yet?” Miriam replies, “Um, maybe? I know I’ve heard of it.” The rest of the country might be surging ahead on a wave of post-war prosperity, but Montana still feels like the rugged land of Zane Grey novels, an Old West inhabited by horsemen, wild mustangs and lonely shepherds.