Before the Fact by Francis Iles

Lina McLaidlaw waits until she is 30 before accepting a marriage proposal from the feckless and irresponsible Johnnie Aysgarth. As head of a fine household and guardian of both the morals and finances of the man she chose to marry, she finds her husband was, and perhaps still is, a killer. "One of the finest studies of murder ever written." ―John C. Farrar