Christie wrote Sleeping Murder and Curtain during World War II to be published after her death. However, unlike Curtain, which concludes the career of her other famous detective Hercule Poirot, there is nothing in the text of Sleeping Murder which indicates it is Marple's last case. Both books were sealed in a bank vault for over thirty years.
The last Marple novel Christie wrote, Nemesis, was published in the 1971, followed by Christie's last novel Postern of Fate. Aware that she would write no more novels, Christie authorized the publication of Curtain in 1975 to send off Poirot. She then arranged to have Sleeping Murder published in 1976, but died before the publication.
"Let sleeping murder lie": This is the motto which is not obeyed by Gwenda Reed (née Halliday), a woman in her early twenties who has recently married and now comes to England to settle down there. She believes her father brought her directly from India to New Zealand when she was a two year-old girl, and she has never been in England. While her husband Giles is still abroad on business, she drives around the countryside looking for a suitable house. She finds an old house in Dillmouth which instantly appeals to her, and she buys it.
After moving in, Gwenda begins to believe that she must be psychic as she seems to know things about the house which she could not possibly know: the location of a connecting door, the pattern of a previous wallpaper, a flight of stairs in the garden, and so on. Becoming increasingly uneasy, she accepts an invitation to go and stay in London with Miss Marple's nephew Raymond West and his wife Joan (who appear also in other stories with Miss Marple). Miss Marple's interest is piqued when, at a performance of John Webster's The Duchess of Malfi, Gwenda screams and flees the theatre for no readily apparent reason, even to herself, when she hears the actor speaking the famous line "Cover her face; mine eyes dazzle; she died young." Gwenda tells Miss Marple later that as she heard those words, she felt she was looking through the banisters, at the dead, blue face of "Helen", listening to someone utter the same line. She insists that she does not know anyone called Helen, and believes she is going mad. Miss Marple suggests that she may be remembering something she witnessed as a small child (looking through rather than over the banisters), and that she may have been in the house that she seemed to know, despite believing that she has never been in England before.
The Reeds and Miss Marple do a bit of research, and discover that Gwenda is not psychic at all, but in fact spent part of her early childhood in the house that she was later to buy. Her young stepmother, Helen, reportedly man-crazy, disappeared, having presumably run off with a man, and her father died. Gwenda was sent to New Zealand to an aunt. The young couple realize that there may be an unsolved crime to investigate. Miss Marple, who first advises the young couple to "let sleeping murder lie", later suggests to her doctor that he prescribe her some sea air, and she travels to Dillmouth.
The investigation that now sets in is completely in the hands of amateurs: Giles and Gwenda Reed and Miss Marple. The amateur sleuths find two old gardeners who remember the Halliday family and some of the old household staff at St Catherine's by placing an ad in several newspapers. The young couple talk to many witnesses. They talk to Dr Kennedy, Helen's half-brother. They do not inform him of Gwenda's memory, and the doctor seems to be nothing more than a loving brother, heartbroken over the disappearance of his very wild younger sister. The police are absent as it has not even been established that a crime has ever been committed; officially, Helen Halliday ran off with one of her lovers and either died abroad or made a clean break with her brother and never contacted anyone at home.
The three men in Helen's life at the time of her disappearance: Walter Fane, a local lawyer, J J Afflick, a local tour guide and Richard Erskine, who resides in the north of England. At one point it seems very likely that one of them must be the murderer: They were all "on the spot", as Miss Marple calls it, that August night eighteen years ago when Helen was murdered. Dr Kennedy deflects the investigation by presenting two letters posted abroad (forged by him, as it turns out later) which he says he got from his half-sister after her disappearance.
When Lily Kimble, who used to be in Halliday's employ, reads an advertisement looking for information about Helen, she senses there could be money in it, and contacts Dr Kennedy to ask for his advice. Kennedy interprets her letter to him as a blackmail attempt. He writes back to her, inviting her to see him at his house and including a train timetable and exact instructions on how to get to his house. He misdirects her to a stretch of woodland, where he strangles her. Then he replaces his original letter with a fake one and is back at his house in time to "wait", together with Giles and Gwenda Reed, for her arrival.
When Lily Kimble's body is found, the police finally start investigating. Now it dawns upon the Reeds that with a murderer still at large, their lives are in danger. This proves true: after Dr Kennedy unsuccessfully tries to poison Gwenda and/or Giles—it is Mrs Cocker, the cook, who takes a sip of the poisoned brandy instead and who consequently has to be hospitalized—Dr Kennedy tries to strangle Gwenda. But Miss Marple has foreseen this; she remained hidden in the house and disables Dr Kennedy by spraying soapy liquid into his face after which policemen appear to arrest him. Miss Marple explains that she believes that Helen was an ordinary, decent young woman, trying to escape from a brother who was pathologically obsessed with her, and that the only evidence of her being "man-mad" came from him. He strangled her to prevent her from living an ordinary, happy life with her husband. Being a learned man, Dr Kennedy was able to hide his condition from the villagers and he staged his sister's death in revenge for her marriage to the man she loved. There are subtle indications that Dr Kennedy had an incestuous desire for his half sister due to some kind of mental illness.
George Thaw in the Daily Mirror of October 22, 1976 said, "Agatha Christie's last novel is very good. Sleeping Murder is the last of Miss Marple's excursions into detection. But perhaps it is her best. Agatha Christie wrote it years ago but if I was going to pick a swansong book this is certainly the one that I would choose. It's her best for years.
Robert Barnard: "Slightly somniferous mystery, written in the 'forties but published after Christie's death. Concerns a house where murder has been committed, bought (by the merest coincidence) by someone who as a child saw the body. Sounds like Ross MacDonald, and certainly doesn't read like vintage Christie. But why should an astute businesswoman hold back one of her better performances for posthumous publication?
Sleeping Murder was filmed by the BBC as a 100-minute film in the sixth adaptation (of twelve) in the series Miss Marple starring Joan Hickson as Miss Marple. It was transmitted in two 50-minute parts on Sunday, January 11 and Sunday, January 18, 1987.
Adapator: Ken Taylor
Director: John Davies
Geraldine Alexander as Gwenda Reed
John Moulder Brown as Giles Reed
Frederick Treves as Dr James Kennedy
Jean Anderson as Mrs. Fane
Terrence Hardiman as Walter Fane
John Bennett as Richard Erskine
Geraldine Newman as Janet Erskine
Jack Watson as Mr. Foster
Joan Scott as Mrs. Cocker
Jean Heywood as Edith Paget
Georgine Anderson as Mrs. Hengrave
Edward Jewesbury as Mr. Sims
David McAllister as Raymond West
Amanda Boxer as Joan West
Esmond Knight as Mr. Galbraith
John Ringham as Dr. Penrose
Eryl Maynard as Lily Kimble
Ken Kitson as Jim Kimble
Kenneth Cope as Jackie Afflick
Peter Spraggon as Detective Inspector Last
Sheila Raynor as Shop assistant
Donald Burton as Bosola
Struan Rodger as Ferdinand
Gary Watson as Major Kelvin Halliday
The novel was adapted as a 90 minute play for BBC Radio 4 and transmitted as part of the Saturday Play strand on December 8, 2001. June Whitfield reprised her role as Miss Marple. It was recorded on October 10, 2001.
Adapator: Michael Bakewell
Producer: Enyd Williams
June Whitfield as Miss Marple
Julian Glover as Dr Kennedy
Beth Chalmers as Gwenda Reed
Carl Prekopp as Giles Reed
Hilda Schroder as Mrs Hengrave
Caroline Pickles as Aunt Alison and Mrs Erskine
Joan Littlewood as Edith
Derek Waring as Richard Erskine
A new adaptation was transmitted on February 5, 2006 as part of ITV's Marple. It starred Geraldine McEwan and Sophia Myles but it had many extreme plot changes. Some of Helen's suitors were not included, whereas a travelling company of performers called The Funnybones was introduced. Also, Dr Kennedy became the half-brother of Claire Kennedy, who was the first wife of Kevin Halliday and who assumed the name of Helen to avoid blackmail. Helen and Claire were different people in the novel.
Geraldine McEwan as Miss Jane Marple
Russ Abbot as Chief Inspector Arthur Primer
Geraldine Chaplin as Mrs. Fane
Phil Davis as Dr. James Alfred Kennedy
Dawn French as Janet Erskine
Martin Kemp as Jackie Afflick
Aidan McArdle as Hugh Hornbeam
Paul McGann as Dickie Erskine
Sophia Myles as Gwenda Halliday
Anna-Louise Plowman as Helen Marsden
Peter Serafinowicz as Walter Fane
Una Stubbs as Edith Pagett
Julian Wadham as Kelvin Halliday
Sarah Parish as Evie Ballantine
Emilio Doorgasingh as Sergant Desai
Harry Treadaway as George Erskine
Richard Bremmer as Mr. Sims
Harriet Walter as Duchess of Malfi
Greg Hicks as Ferdinand
Mary Healey as Shop Assistant
Helen Coker as Lily Tutt
Nickolas Grace as Lionel Luff
Vince Leigh as Jim Tutt
Darren Carnall as Dresser