Who Pays the Piper? (The Ernest Lamb Mysteries)

A blackmailing businessman turns up dead in this gripping mystery from the creator of the beloved Miss Silver
 
Lucas Dale always gets what he wants. And this time he wants another man’s fiancée: Susan Lenox. Never mind that she’s engaged to Bill Carrick, an up-and-coming architect without a farthing to his name. Cathleen O’Hara, Dale’s mousy social secretary, serves as the unwitting instrument of his plan, and a nasty blackmail scheme is set in motion. Soon, Susan has no choice but to break off her engagement and agree to marry Dale—until he’s found in his study with a bullet in his head.
 
Scotland Yard is called in, and before long, Inspector Ernest Lamb and Detective Frank Abbott have a suspect: Carrick. But as Lamb and Abbott dig deeper, they discover others with means, motive, and opportunity, including the victim’s penniless former wife who was handy with a gun, and his American business partner who wanted the money Dale owed him. No one has an alibi for the time of Dale’s demise. And someone else will die before the price of murder is paid.
 
Who Pays the Piper? is the 2nd book in the Ernest Lamb Mysteries, but you may enjoy reading the series in any order.