Dead Man's Folly is a work of detective fiction by Agatha Christie and first published in the US by Dodd, Mead and Company in October 1956 and in the UK by the Collins Crime Club on November 5 of the same year. The US edition retailed at $2.95 and the UK edition at twelve shillings and sixpence (12/6). It features Hercule Poirot, her famous Belgian detective, and Ariadne Oliver. The house where the story is set was based on Christie's Devon home, Greenway House.
En route to Nasse House Poirot gives a lift to two female hitch-hikers – one Dutch and one Italian – who are staying at the youth hostel adjoining the Nasse House grounds. When he arrives, Mrs. Oliver explains that she feels that her plans for the Murder Hunt have been, almost imperceptibly, influenced by the advice that she has been given by people in the house, until it is almost as though she is being pushed into staging a real murder.
The owner of Nasse House is George Stubbs, a wealthy man who has seemingly adopted the false title of “Sir” in order to confirm his position in the local community. His much younger wife is the seemingly simple and impressionable Hattie, a young woman who has apparently been introduced to him by Amy Folliat, the surviving member of the family that once owned the house. Now that her sons have been supposedly killed during the War, she is living out her days in the Lodge House. Other visitors at Nasse House include an architect, Michael Weyman, who criticises the siting some years earlier of a folly in an inappropriate area of the grounds.
On the day of the fête, Hattie learns that a cousin, Etienne de Sousa, is about to visit, and she seems upset by this, referring to him as a killer. At the fete, a local Girl Guide, Marlene Tucker, is to play the part of the victim, and she waits in the boathouse to play her role when someone approaches her. Poirot observes the movements of some of the visitors to the house. Later, in the company of Mrs. Oliver, he discovers the corpse of Marlene in the boathouse. Moreover, Hattie is discovered to have gone missing. Both the police and Poirot himself are initially baffled.
The investigation focuses on Etienne de Sousa, a wealthy young man who shows no apparent concern at Hattie’s disappearance and has arrived in perfect time to have committed the murder. Another suspect is Amanda Brewis, George’s secretary, who appears to be in love with Sir George and claims to have been sent down to the boathouse by Hattie with refreshments for Marlene at around the time that the girl was killed. This sounds very out of character for Hattie. Further confusion is added by the behaviour of the Legges, who appear to have some sort of shady connection with a young man in a turtle shirt who has been seen in the grounds. (It later comes to light that this red herring is connected with Legge’s career as a nuclear physicist.)
Poirot’s attention is directed to Amy Folliat, who seems to know more than she is saying. After the boatman Merdell dies, Poirot discovers that he was Marlene’s grandfather. Now he puts together several stray clues: Marlene had said that her grandfather had seen someone burying a woman in the woods; Marlene was the type to blackmail, and had in fact received small sums of money prior to her murder; Merdell had commented significantly to Poirot that there would "always be Folliats at Nasse House".
In the denouement Poirot reveals that George Stubbs is none other than Amy Folliat’s younger son, James, who had gone missing but had not died during the War. Instead, Amy had paired him with the impressionable, but very wealthy, Hattie, enabling him to fleece her of her money and establish his new identity, buying the family house and ensuring the continuity of Folliat possession. Unbeknownst to Amy, however, George/James was already married, and as soon as he had possession of Nasse he killed Hattie, and substituted his first wife, a young Italian, in her place. She was buried in the ground that was later secured by building the folly.
Marlene had guessed the secret from hints dropped by her grandfather, and George and his real wife decided it would be safer to kill her than continue giving her hush money. The day before the day of the murder, "Hattie" began to establish another identity as an Italian hitch-hiker. On the day of the murder, she switched between the two roles, killing Marlene and escaping the grounds as the hitch-hiker, with Hattie’s clothes in her rucksack. The day of the murder had been selected to cast suspicion upon Etienne, who had actually notified them some weeks earlier of his visit.
George/James is not seen at the end of the novel, which instead focuses on the despair of his mother.
The review in The Times of November 15, 1956 was somewhat damning; "Dead Man's Folly is not Miss Agatha Christie at her best. The murder and the solution of it are ingenious, but then, with Miss Christie, they always are, and it is pleasant to watch M. Hercule Poirot at work again. The character drawing is flat and facile, however, and the dialogue, always Miss Christie's weak point, disastrous.
Maurice Richardson of The Observer of November 18, 1956 pointed out the similarity between the house portrayed in the book and Christie's own and summed up, "Stunning but not unguessable solution. Nowehere near a vintage Christie but quite a pleasing table-read.
Robert Barnard: "Highly traditional recipe, but not done with the same conviction as in the 'thirties. Nobody much is what they seem, and old sins cast long shadows. Mrs Oliver looms large here, as she was frequently to do from now on, both in Poirot books and in others.
The novel was first serialised in the US in Collier's Weekly in three abridged instalments from July 20 (Volume 138, Number 2) to August 17, 1956 (Volume 138, Number 4) with illustrations by Robert Fawcett.
In the UK the novel was first serialised in the weekly magazine John Bull in six abridged instalments from August 11 (Volume 100, Number 2615) to September 15, 1956 (Volume 100, Number 2620) with illustrations by "Fancett.