A Little Less Than Kind — Charlotte Armstrong

David Crown, a robust, practical man in his fifties, had finally achieved everything he ever wanted in life: the presidency of a large corporation, a luxurious mansion in Pasadena, and marriage to the lovely, sensitive Abby -- all made possible by the death of his best friend -- Abby's husband. Only Ladd -- Abby's handsome son -- found the new arrangement less than ideal. Ladd thought it all very curious... and suspicious. Could it all be just "chance"? Discovering a cryptic, scrawl in his father's diary, Ladd determined to unravel it.