Oh, Murderer Mine — Norbert Davis

Doan, a chubby private eye with a fondness for weak women and strong drink, and Carstairs, his enormous Great Dane sidekick, have been hired by 54-year-old but still glamorous beauty maven Heloise of Hollywood to make sure that no young lovely tries to steal her 26-year-old hunk of a husband, Eric Trent. Originally published in 1946.