You Live Once — John D. MacDonald

Clint Sewell knew there wasn't a wife within fifty miles who didn't have reason to murder Mary Olan - because there wasn't a husband around who didn't think the grass was greener in Mary Olan's bedroom. The latest occupant was Sewell's boss, Dodd Raymond - a man not above using Sewell to cover up his sins. And maybe not above letting Clint take the rap when the fabulous Mary is found dead in Sewell's bedroom closet with his belt around her neck.