Shoot to Kill — Brett Halliday

Mike Shayne investigates the connection between a flirtatious wife, a husband blinded by jealousy, and a murdered boss

Just 3 years ago, Ralph Larson and his wife were newlyweds, the happiest young couple in Miami. But since Larson went to work for Wesley Ames, his life has been hell. He's convinced his wife has fallen in love with his boss, and the jealousy is driving him mad. Hoping to avoid a murder, private detective Mike Shayne tells Larson's wife to knock off the flirting before her husband's envy leads to tragedy. But it's too late: Death is at the door.
 
When Shayne learns that Larson is headed to Ames's apartment, pistol in hand, he races there hoping to prevent bloodshed. He finds Larson standing over his boss's corpse, ready to confess to murder. But there's more here than meets the eye -- and more to this murder than a resentful husband holding a smoking gun.
 
Shoot to Kill is the 48th book in the Mike Shayne Mysteries, but you may enjoy reading the series in any order.