[14]: 9–10, 86–88  She eventually made friends with other girls in Torquay, noting that "one of the highlights of my existence" was her appearance with them in a youth production of Gilbert and Sullivan's The Yeomen of the Guard, in which she played the hero, Colonel Fairfax.

From October 1914 to May 1915, then from June 1916 to September 1918, she worked 3,400 hours in the Town Hall Red Cross Hospital, Torquay, first as a Voluntary Aid Detachment nurse (unpaid) then as a dispenser at £16 (approximately equivalent to £1,130 in 2023) a year from 1917 after qualifying as an apothecary's assistant.

[6]: 73–74 Christie had long been a fan of detective novels, having enjoyed Wilkie Collins's The Woman in White and The Moonstone, and Arthur Conan Doyle's early Sherlock Holmes stories.

It featured Hercule Poirot, a former Belgian police officer with "magnificent moustaches" and a head "exactly the shape of an egg",[32]: 13  who had taken refuge in Britain after Germany invaded Belgium.

[47] On 14 December 1926, she was located at the Swan Hydropathic Hotel in Harrogate, Yorkshire, 184 miles (296 km) north of her home in Sunningdale, registered as "Mrs Tressa[d] Neele" (the surname of her husband's lover) from "Capetown [sic] S.A." (South Africa).

[69][70] The British intelligence agency MI5 investigated Christie after a character called Major Bletchley appeared in her 1941 thriller N or M?, which was about a hunt for a pair of deadly fifth columnists in wartime England.

The agency's fears were allayed when Christie told her friend, the codebreaker Dilly Knox, "I was stuck there on my way by train from Oxford to London and took revenge by giving the name to one of my least lovable characters.

Thirty wreaths adorned Christie's grave, including one from the cast of her long-running play The Mousetrap and one sent "on behalf of the multitude of grateful readers" by the Ulverscroft Large Print Book Publishers.

[82][94] Her remaining 36% share of Agatha Christie Limited was inherited by Hicks, who passionately preserved her mother's works, image, and legacy until her own death 28 years later.

[114] Thompson believes Christie's occasional antipathy to her creation is overstated, and points out that "in later life she sought to protect him against misrepresentation as powerfully as if he were her own flesh and blood".

[32]: 375  In a recording discovered and released in 2008, Christie revealed the reason for this: "Hercule Poirot, a complete egoist, would not like being taught his business or having suggestions made to him by an elderly spinster lady.

This included Naomi Alderman, Leigh Bardugo, Alyssa Cole, Lucy Foley, Elly Griffiths, Natalie Haynes, Jean Kwok, Val McDermid, Karen M. McManus, Dreda Say Mitchell, Kate Mosse and Ruth Ware.

[124] Author Dilys Winn called Christie "the doyenne of Coziness", a sub-genre which "featured a small village setting, a hero with faintly aristocratic family connections, a plethora of red herrings and a tendency to commit homicide with sterling silver letter openers and poisons imported from Paraguay".

[126][127] Christie did not limit herself to quaint English villages – the action might take place on a small island (And Then There Were None), an aeroplane (Death in the Clouds), a train (Murder on the Orient Express), a steamship (Death on the Nile), a smart London flat (Cards on the Table), a resort in the West Indies (A Caribbean Mystery), or an archaeological dig (Murder in Mesopotamia) – but the circle of potential suspects is usually closed and intimate: family members, friends, servants, business associates, fellow travellers.

[128]: 37  Stereotyped characters abound (the femme fatale, the stolid policeman, the devoted servant, the dull colonel), but these may be subverted to stymie the reader; impersonations and secret alliances are always possible.

"[133]: 135–36 On BBC Radio 4's Desert Island Discs in 2007, Brian Aldiss said Christie had told him she wrote her books up to the last chapter, then decided who the most unlikely suspect was, after which she would go back and make the necessary changes to "frame" that person.

"[14]: 457  Critics agreed she had succeeded: "The arrogant Mrs. Christie this time set herself a fearsome test of her own ingenuity ... the reviews, not surprisingly, were without exception wildly adulatory.

Christie's British literary agent later wrote to her US representative, authorising American publishers to "omit the word 'Jew' when it refers to an unpleasant character in future books.

Poirot and Miss Marple mysteries written between 1920 and 1976 have had passages reworked or removed in new editions published by HarperCollins, in order to strip them of language and descriptions that modern audiences find offensive, especially those involving the characters Christie's protagonists encounter outside the UK.

[139] In addition to Hercule Poirot and Miss Marple, Christie also created amateur detectives Thomas (Tommy) Beresford and his wife, Prudence "Tuppence" née Cowley, who appear in four novels and one collection of short stories published between 1922 and 1974.

[32]: 118–19  The 12 short stories which introduced him, Parker Pyne Investigates (1934), are best remembered for "The Case of the Discontented Soldier", which features Ariadne Oliver, "an amusing and satirical self-portrait of Agatha Christie".

"[143] She next adapted her short radio play into The Mousetrap, which premiered in the West End in 1952, produced by Peter Saunders and starring Richard Attenborough as the original Detective Sergeant Trotter.

"[133]: 208  Reflecting a juxtaposition of innocence and horror, numerous Christie titles were drawn from well-known children's nursery rhymes: And Then There Were None (from "Ten Little Niggers", a rhyme also published as "Ten Little Indians", both of which were also used for the book's title in some printings),[154] One, Two, Buckle My Shoe (from "One, Two, Buckle My Shoe"), Five Little Pigs (from "This Little Piggy"), Crooked House (from "There Was a Crooked Man"), A Pocket Full of Rye (from "Sing a Song of Sixpence"), Hickory Dickory Dock (from "Hickory Dickory Dock"), and Three Blind Mice (from "Three Blind Mice").

[16]: 430–31 She felt differently about the 1974 film Murder on the Orient Express, directed by Sidney Lumet, which featured major stars and high production values; her attendance at the London premiere was one of her last public outings.

"[129]: viii  There were to be many medical practitioners, pharmacists, and scientists, naïve or suspicious, in Christie's cast of characters; featuring in Murder in Mesopotamia, Cards on the Table, The Pale Horse, and Mrs. McGinty's Dead, among many others.

[128]: 269  Archaeologists and experts in Middle Eastern cultures and artefacts featured in her works include Dr Eric Leidner in Murder in Mesopotamia and Signor Richetti in Death on the Nile.

[204]: 187, 226–27 After the Second World War, Christie chronicled her time in Syria in Come, Tell Me How You Live, which she described as "small beer – a very little book, full of everyday doings and happenings".

[205]: (Foreword)  From 8 November 2001 to March 2002, The British Museum presented a "colourful and episodic exhibition" called Agatha Christie and Archaeology: Mystery in Mesopotamia which illustrated how her activities as a writer and as the wife of an archaeologist intertwined.

A young Agatha is depicted in the Spanish historical television series Gran Hotel (2011) in which she finds inspiration to write her new novel while aiding local detectives.

[215] Andrew Wilson has written four novels featuring Agatha Christie as a detective: A Talent For Murder (2017), A Different Kind of Evil (2018), Death In A Desert Land (2019) and I Saw Him Die (2020).