I recommend Mucho Mojo, by award-winning writer Joe R. Lansdale. It's the second book in a series, but it isn't crucial to read Savage Season first, and Mucho Mojo is a better mystery story. Lansdale has written some comics, as well as several episodes of Batman: the Animated Series, and quite a few novels and short stories.
Mucho Mojo features two very unconventional sleuthes, Hap Collins and his best friend Leonard Pine. Hap is middle-aged good old boy from east Texas with some martial arts skills. Leonard is too, and he is also an african-american, homosexual Vietnam vet. Leonard's favorite uncle has died, and left behind a house, some money and a mystery for Leonard and Hap. The story addresses some serious issues, mixed in with action, grit and wit.