In this 1967 book about Superintendent Adam Dalgliesh of Scotland Yard, he is on vacation to the coast to spend some time with his aunt, a famous ornithologist, and unwind from a brutal murder case. Unfortunately, he gets little rest, when one of the writers in the area is found dead in a boat with his hands chopped off. While not his case (he doesn't really want it anyway), the local Inspector does ask for his some of his help, while keeping him in the dark about the whole case.
The victim, Maurice Seton, a detective writer and victim, was last seen on Tuesday night in London getting out of a cab at Paddington Station. All of the characters, Langtham, a theater critic who was with a woman that night, Bryce, who suffered an asthma attack and had to call the doctor twice in London, Miss Calthrop who was with a friend and at home in the small town, her niece Eliza Marley, who was secretly staying in a hotel in London, and Sylvia Kedge, the cripple, who walked with leg braces and crutches and worked for Seton as a cleaning woman and typist, was at home all night, his half-brother Digby, who inherits his fortune, was thrown in the drunk tank Tuesday night and then was in a car accident on Wednesday after receiving a mysterious call saying his brother had been found dead and to come to the police station. Everyone has an alibi for when the murder took place, but not everybody has an alibi for when the body was pushed in the boat on Wednesday night into the water.
Surprisingly, the death is ruled as being by natural causes, but Dalgliesh doesn't buy it and soon figures out how a natural death can actually be a murder, if done right. But it will be hard to prove, as he tells the Inspector after Digby is found poisoned on the beach. Why was he killed? He had no one to leave his new money to--money that he would only receive once he married--the rest to be held in a trust. Add to that, Seton was planning on changing his will to leave a little bit to Digby, Sedge, and Miss Calthrop, and the majority to a writing prize in his name.
There's also the mystery of the two manuscripts that arrive at his house, one while he was presumably still alive, but not in his writing style, and another a day later, when he was dead, that could have been written by him. The second describes a scene where a body is found in a boat with its hands chopped off. Miss Calthrop admits to giving Seton that idea for a book, but who else knew about it and would play such a sick joke?
This book confounded me, especially when the M.E. ruled the death natural causes. If he died of a heart attack (he had a weak heart), then why were his hands cut off and his body placed in the boat? And everyone has an alibi for the time of the murder, but not necessarily for the time of the mutilation and placing in the boat. I was completely surprised by the ending. I really didn't see it coming, it was so calculated and precise of a murder, one could easily walk away a free person, since there was no proof otherwise. Brilliant!
…it came to him that he had got what he wanted at almost the precise moment of suspecting that he no longer wanted it.
--P.D. James (Unnatural Causes p10)
Link to Amazon: https://www.amazon.com/Unnatural-Causes-Adam-Dagliesh-Mystery/dp/0743219597/ref=sr_1_1?s=books&ie=UTF8&qid=1467376667&sr=1-1&keywords=Unnatural+causes