Warlock by Jim Harrison

Johnny Lundgren, a.k.a. Warlock, is an unemployed foundation executive who, after surviving a midlife crisis, finally decides to get a job. Warlock soon gets hired by a crazy, but genius doctor as a trouble-shooter, where he's tasked with everything battling poachers in the haunted wilderness of northern Michigan to investigating his employer's wife and son in the seamy underside of Key West. A comedy with one foot in the abyss, Warlock is what the New York Times called "farcical, reflective, luscious, gritty" entertainment from one of this country's most beloved authors.