Rex Fortescue, Adele Fortescue, and Gladys Martin all die within a few hours. Rex was poisoned by Taxine, a poisonous constituent of yew plants, Adele was poisoned by potassium cyanide, and Gladys was strangled.
Miss Marple arrives at Yewtree Lodge, the home of the Fortescues where Gladys was a maid, about 2/5ths of the way through the book. Miss Marple gave instruction to Gladys about how to become a servant and not unnaturally was distressed when she read of Gladys’s death.
Inspector Neele is already on the case from Scotland Yard and is well on his way to solving the case, but Miss Marple gives him a nudge in the right direction at the appropriate time.
Of course, very few of the characters are being completely honest and in order to solve this you have to think the worst of people.
Rex Fortescue has two sons and a daughter. The two sons are away, one called Percival is returning from a business trip to the north of England and the other is returning from East Africa with his wife. Percival lives with his wife at Yewtree Lodge. The daughter, Elaine, lives at Yewtree Lodge and her fiance is staying at a nearby hotel.
Adele Fortescue is Rex Fortescue’s second wife and is thirty years younger than him. She has a lover who is staying in a nearby hotel. The sister of Rex Fortescue’s first wife also lives at Yewtree Lodge.
There is also Mary Dove, the housekeeper, who appears too efficient to be true, plus Mr and Mrs Crump the buttler and cook.
Rex Fortescue is found to have a pocket full of rye, Adele Fortescue was eating bread and honey when she died, and Gladys was gathering in the washing, all of which is in keeping with the nursery rhyme Sing a Song of Sixpence.
There is also the mysterious Blackbird Mine in Africa. Rex Fortescue allegedly murdered a business partner called MacKenzie in a dispute about the mine. Mrs MacKenzie is in a nursing home close by but all trace has been lost of her two children, one male and one female. Where could they be?