Grave Mistake

 Grave Mistake by Ngaio Marsh (1978) 256 pages

Twice-widowed Sybil Foster meets a handsome doctor and goes to stay at a spa where he works. Meanwhile, her first husband's son, Claude, has arrived on scene asking for money and appears to be involved in dubious activities, perhaps drugs and blackmail. Sybil's daughter, Prunella, becomes engaged to a very wealthy man's son, Gideon, which upsets Sybil because she wants Prunella to marry someone else. When Sybil is found dead in the spa, it's first assumed to be suicide,  which doesn't make sense to anyone who knows her. When it is revealed that her will was recently changed to benefit her doctor and her gardener, more investigation is needed. 

Chief Superintendent Roderick Alleyn arrives on the scene with his trusty crew to find out what really happened to Sybil. It's a fun read, with everyone looking, in turn, both innocent and guilty.