Poirot forms a "Legion" of relatives of the deceased to uncover new information: Franklin Clarke, Sir Carmichael's brother; Mary Drower, Ascher's niece; Donald Fraser, Betty's fiancé; Megan Barnard, Betty's elder sister, and Thora Grey, Sir Carmichael's young assistant.

sends his next letter, directing everybody to Doncaster, where it is suspected that the next murder will occur at the St. Leger Stakes race meeting that day.

The police soon get a tip-off about the man linked to the murders – Alexander Bonaparte Cust, an epileptic travelling salesman, who suffers from memory blackouts and constant agonising headaches as the result of a head injury during the First World War.

A chance encounter with Cust at a pub gave Franklin the idea for the murder plot – he would disguise his crime as part of a serial killing.

A suggestion by Hastings makes clear that the third letter was misaddressed intentionally because Franklin wanted no chance of the police interrupting that murder.

Franklin laughs off Poirot's theory but panics when he is told that his fingerprint has been found on Cust's typewriter key and that Milly Higley, a co-worker of Betty Barnard, saw him in her company.

The Times Literary Supplement on 11 January 1936 concluded, with a note of admiration for the plot that, "If Mrs Christie ever deserts fiction for crime, she will be very dangerous: no one but Poirot will catch her.

"[4] In The Observer's issue of 5 January 1936, "Torquemada" (Edward Powys Mathers) wrote, "Ingenuity ... is a mild term for Mrs Christie's gift.

"[5] E R Punshon reviewed the novel in 1936, writing that "Some readers are drawn to the detective novel by the sheer interest of watching and perhaps anticipating the logical development of a given theme, others take their pleasure in following the swift succession of events in an exciting story, and yet others find themselves chiefly interested in the psychological reactions caused by crime impinging upon the routine of ordinary life.

But the wise reader, remembering other tales of Mrs Christie's, will murmur to himself 'I trust her not; odds on she is fooling me,' and so will continue to a climax it is not 'odds on' but a dead cert he will not have guessed.

To an easy and attractive style and an adequate if not very profound sense of character Mrs Christie adds an extreme and astonishing ingenuity, nor does it very greatly matter that it is quite impossible to accept the groundwork of her tale or to suppose that any stalking-horse would behave so invariably so exactly as required.

"[8] An unnamed reviewer in the Daily Mirror of 16 January 1936 said, "I'm thanking heaven I've got a name that begins with a letter near the end of the alphabet!

He noted that the plot "differs from the usual pattern in that we seem to be involved in a chase: the series of murders appears to be the work of a maniac.

In fact the solution reasserts the classic pattern of a closed circle of suspects, with a logical, well-motivated murder plan.

In the same chapter, Poirot mentions his failed attempt at retirement to grow vegetable marrows as depicted in The Murder of Roger Ackroyd.

In Chapter 19, Poirot reflects over his first case in England, where he "brought together two people who loved one another by the simple method of having one of them arrested for murder".

[11] Chapters 393–397 of Gosho Aoyama's manga Detective Conan feature a case with some similarities as the criminal was inspired by the plot of The A.B.C.

The 1998 anime film Case Closed: The Fourteenth Target is a combination of this story, with a murderer killing based on numbers in names as a ruse to confuse detectives, while also incorporating Christie's And Then There Were None.

[13] The first adaptation of the novel was the 1965 film The Alphabet Murders with Tony Randall as Hercule Poirot, a version far more comic than mysterious.

The BBC Radio adaptation Poirot – The ABC Murders starring John Moffatt and Simon Williams was first broadcast in 2000.

[16] In 1992, the novel was adapted for television as part of ITV's Agatha Christie's Poirot, and was first aired in the UK on 5 January 1992.

[citation needed] The first aired episode of the French television series Les Petits Meurtres d'Agatha Christie was an adaptation of The A.B.C.

[17] It stars John Malkovich as Hercule Poirot and Rupert Grint as Inspector Crome,[18][19] with guest stars including Eamon Farren as Alexander Bonaparte Cust, Jack Farthing as Donald Fraser, Freya Mavor as Thora Grey, Kevin McNally as Inspector Japp, and Anya Chalotra as Lily Marbury.

[20] This adaptation only loosely follows the novel's plot, and features considerable changes to both story and character: A four-part episode of the anime Agatha Christie's Great Detectives: Poirot and Marple is based on the book.

[citation needed] In 2009, DreamCatcher Interactive released a video game version of the novel for the Nintendo DS titled Agatha Christie: The ABC Murders.

The game has players control Captain Hastings and must solve the mystery by inspecting crime scenes and questioning suspects.

Murders occurred in the US, when an abridged version appeared in the November 1935 (Volume XCIX, Number 5) issue of Cosmopolitan magazine with illustrations by Frederic Mizen.