The novel follows the eponymous murders and their investigation as seen by Arthur Hastings, Poirot's old friend. Poirot receives typed letters signed by A.B.C.. In each is given the date and location of the next murder. A.B.C. moves alphabetically: Alice Ascher is a tobacco shop owner killed in her shop in Andover, Betty Barnard is a flirty waitress killed in Bexhill, and Sir Carmichael Clarke is a wealthy man killed at his home in Churston. A.B.C. leaves an ABC railway guide with each victim. Poirot has two doubts in his mind: a) Why would A.B.C. write to him instead of the Scotland Yard or any reputed newspaper?, and b) Why did a meticulous man like A.B.C. misspell Poirot's address on the Churston letter?
Each chapter narrated by Hastings is followed by a description of events in the life of Alexander Bonaparte Cust, a travelling salesman. Cust, an epileptic who had served in the war, was rendered incapable of doing many kinds of work due to a head injury which made him prone to memory blackouts and constant headaches. Meanwhile, Poirot forms a "Legion" of relatives of the deceased in hopes of uncovering new information. Inspector Crome, who doubts Poirot's detective abilities and Dr Thomson, who tries to profile this serial killer, are part of the police team.
After a meeting with the third victim's widow, Lady Clarke, Poirot recognises one feature common to all three of the murders: a man selling silk stockings had appeared at or near to the crime scene, on the day of each murder. He had sold a pair of stockings to Mrs Ascher and to Mrs Barnard, while being sent away without a sale from the Clarke home. A.B.C. sends his next letter, directing everybody to Doncaster. As the St. Leger horse race will take place that day, Poirot hopes to find him on the race course. But A.B.C. strikes in a cinema hall instead, killing George Earlsfield, instead of Roger Emmanuel Downes, a logical victim sitting only two seats away. However, Cust, of whom neither Poirot nor his Legion are aware, slips out of the cinema hall unnoticed, after suffering a blackout. Cust, who has no idea of the happenings, finds the murder weapon in his pocket and blood on his sleeve, and realises the implications.
Lily, daughter of Cust's landlady, tips Cust off, and he tries to flee, but collapses at the Andover police station. Tom Hartigan, Lily's boyfriend, informs Inspector Crome of his suspicions regarding Cust; when taken into custody, Cust lacks memory of the murder, but believes he must be guilty. A search of his rooms finds silk stockings, lists of clients, the fine paper of A.B.C.'s letters to Poirot, an unopened box of ABC railway guides, and in the hall, the still-bloody knife used in the last murder. The police find that Cust was never hired by the stocking firm, and that the letters to Poirot had been typed on the typewriter Cust claimed had been given him by the firm. Poirot meets Cust, but doubts his guilt after hearing Cust's full story; Cust has a solid alibi for the Bexhill murder, and has no recollection of any of the murders. Poirot calls a Legion meeting. He categorically proves that Cust is not the murderer. Early on, in discussing the Churston letter, Hastings had suggested that the letter had been meant to go astray. Poirot realises this simple solution is the correct one. The murderer wanted no chance of the police interrupting that murder. Poirot reveals that A.B.C. is Franklin Clarke, brother of victim C, Sir Carmichael Clarke, heir to the Clarke estate, and a member of Poirot's assembled Legion.
Franklin feared that after Lady Clarke's death, which was imminent, Carmichael would marry Thora Grey, his young, attractive assistant. Should such have happened, the Clarke estate would instead go to Thora, and any children she might have with Carmichael. Franklin decides to kill his brother while Lady Clarke is alive and make it look like a serial killing to throw off suspicion. Cust and Franklin met in a chance encounter in a pub, which gave Franklin the idea for the A.B.C. murder plot. He then planned and executed everything so that Cust would be framed—serving as his stalking horse.
Franklin laughs off Poirot's claims, but panics when Poirot states that his fingerprint was found on Cust's typewriter key, and that Franklin had been recognised by Milly Higley, while Franklin was in Betty's company. Franklin tries to shoot himself using his own gun, but Poirot has already had the gun emptied with help of a pickpocket. The police apprehend him. With the case finally solved, Poirot pairs off Donald, once engaged to Betty, and Megan, Betty's elder sister. Cust tells Poirot of an offer from the press to sell his story, Poirot suggests that he demand a higher price for it, and goes on to suggest that Cust's headaches may arise from his spectacles. Poirot tells Hastings that the fingerprint on the typewriter was a bluff. Poirot is pleased that he and Hastings "went hunting once more".A. B. C. – unknown cold-blooded serial killer and Poirot's nemesis in this novel. He kills his victims in alphabetical order and leaves an ABC railway guide depicting the scene of crime as his calling card.
Alexander Bonaparte Cust – oddly-named travelling salesman; he sells stockings and is epileptic. He fought in the war, and received a blow on head, making him prone to blackouts and severe headaches.
Alice Ascher – the first victim, an old woman estranged from her husband, with no children, running a tobacco shop in Andover.
Franz Ascher – Alice's alcoholic husband; initially but briefly a suspect in his estranged wife's murder.
Elizabeth "Betty" Barnard – the second victim, a young, flirtatious part-time waitress in Bexhill.
Megan Barnard – Betty's elder, sensible and comparatively down to earth sister and later a member of the Legion assisting Poirot in the investigation.
Milly Higley – co-worker of Betty Barnard, albeit a plain looking one.
Sir Carmichael Clarke – ABC's third victim, a rich old man in Churston. Sir Carmichael is a childless man with a cancer-stricken wife.
Lady Charlotte Clarke – terminally ill widow of Sir Carmichael; dying of cancer, she takes various drugs which often render her delusional and/or irritated, but she does provide a vital clue to Poirot.
Franklin Clarke – Sir Carmichael's aggrieved younger brother and immediate successor; a member of the Legion, it is due to him that others decided to help Poirot.
Inspector Crome – assigned to the Bexhill murder; has a low opinion of Poirot.
Roger Downes – schoolteacher present at a cinema in Doncaster. Although Downes would seem to be the logical victim, George Earlsfield was killed instead; Downes was sitting just two seats away and is the one who discovered Earlsfield's body.
Mary Drower – Alice Ascher's niece; also a Legion member.
George Earlsfield – the fourth victim at a cinema in Doncaster; a barber by trade.
Donald Fraser – Betty's would-be fiancé; temperamental and an initial suspect in Betty's murder; also part of the Legion.
Thora Grey – Sir Carmichael Clarke's attractive young assistant; also part of the Legion.
Tom Hartigan – boyfriend of Lily Marbury, whose mother rents a room to Cust. He saw Cust in Euston station with a ticket to Doncaster, and got suspicious when Lily said Cust reported he was going to Cheltenham, reached from Paddington station.
Hercule Poirot – renowned Belgian detective famous for solving cases using his "little grey cells".
Captain Arthur Hastings – Poirot's old friend and companion on the case; an impatient man, his lack of imagination is often playfully ridiculed by Poirot.
Detective Chief Inspector James Harold Japp – another old friend of Hercule Poirot, who is assigned the case.
Lily Marbury – Soft-hearted daughter of Cust's landlady. She warned Cust after Tom Hartigan told the police of Cust's actions.
Dr Thompson – forensic psychologist who tries to make a profile of the killer.
The Times Literary Supplement of 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."
Isaac Anderson in The New York Times Book Review of 16 February 1936 finished his review by stating, "This story is a baffler of the first water, written in Agatha Christie's best manner. It seems to us the very best thing she has done, not even excepting Roger Ackroyd.
In The Observer's issue of 5 January 1936, "Torquemada" (Edward Powys Mathers) said, "Ingenuity ... is a mild term for Mrs Christie's gift. In The A.B.C. Murders, rightly chosen by the [crime] club as its book of the month, she has quite altered her method of attack upon the reader, and yet the truth behind this fantastic series of killings is as fairly elusive as any previous truth which Poirot has had to capture for us. The reader adopts two quite different mental attitudes as he reads. At first, and for a great many pages, he is asking himself: "Is Agatha Christie going to let me down? Does she think she can give us this kind of tale as a detective story and get away with it?" Then the conviction comes to him that he has been wronging the authoress, and that he alone is beginning to see through her artifice. In the last chapter he finds, because brilliant circus work with a troop of red horses and one dark herring has diverted his attention from a calm consideration of motive, he has not been wronging, but merely wrong. It is noticeable, by the way, that characters break off at intervals to tell us that we have to do with "a homicidal murderer". We are ready to take this for granted until Mrs Christie (I wouldn't put it past her) gives us one who isn't."
E. R. Punshon reviewed the novel in the 6 February 1936 issue of The Guardian when he said, "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. Skilful and happy is that author who can weave into a unity this triple thread. In Mrs Agatha Christie's new book...the task is attempted with success." He added, "In the second chapter, Mrs Christie shows us what seems to be the maniac himself. 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. As at Bexhill, a hitch would always occur. In the smooth and apparently effortless perfection with which she achieves her ends Mrs. Christie reminds one of Noël Coward; she might, indeed, in that respect be called the Noël Coward of the detective novel."
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! That's just in case some imitative soul uses this book as a text book for some nice little series of murders." They summed up, "It's Agatha Christie at her best."
Robert Barnard: "A classic, still fresh story, beautifully worked out. It 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. The English detective story cannot embrace the irrational, it seems. A total success – but thank God she didn't try taking it through to Z."
In the "Binge!" article of Entertainment Weekly Issue #1343-44 (26 December 2014–3 January 2015), the writers picked The A.B.C. Murders as an "EW favorite" on the list of the "Nine Great Christie Novels".
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 story of the 2012 Malayalam film Grandmaster draws inspirations from The A.B.C. Murders. The characterisation of Chandrasekhar in the movie is played by Indian movie veteran Mohanlal is also inspired from Hercule Poirot, the protagonist of the novel.
The BBC Radio adaptation Poirot – The ABC Murders starring John Moffatt and Simon Williams. First broadcast on BBC Radio 7 Saturday, 22 March 2008. Currently rebroadcast on BBC Radio 4 Extra.
The novel was adapted in 1992 for the television series Agatha Christie's Poirot with David Suchet playing the role of Hercule Poirot. The adaptation remains faithful to the novel, with some minor changes and characters omitted. In the end the murderer tries to escape while in the novel, he tries to commit suicide. The cast included:Hugh Fraser as Captain Hastings
Philip Jackson as Chief Inspector Japp
Donald Sumpter as Alexander Bonaparte Cust
Donald Douglas as Franklin Clarke
Nicholas Farrell as Donald Fraser
Pippa Guard as Megan Barnard
It first aired on 5 January 1992 in the UK.
This production includes scenes from two movies watched by Cust. The first is a sentence from the 1939 movie Black Limelight (known as Footsteps in the Sand in USA) starting with the line "You've been very careful, but you made one mistake. It'll be the first time that anyone has suggested you as the murderer. You'll be watched, you'll be questioned, you'll be followed, you'll give yourself away, and they'll get you." Cust views a scene from another Hitchcock film in the Doncaster cinema, about 1:10 into the episode: he sees the closing minutes of the 1932 film Number 17, where in the second-last scene of that film, a train crashes into a ferry and then into the sea.
A four-part episode of the anime Agatha Christie's Great Detectives: Poirot and Marple is based on the book.
The A.B.C. Murders are also an arc of the anime "Hyouka", or episode 15 "The Jūmonji Case" of Hyōka video series.
'ABC Satsujin Jiken' (ABC殺人事件, The ABC Murders) is a two volume manga by Yasushi Hoshino loosely based on a mixture of the original novel and Murder in the Mews. Set in Japan, Poirot retains his iconic appearance though is renamed Eikubo while Hastings is renamed Asakura.
In 2009, DreamCatcher Interactive released a video game version of the novel for the Nintendo DS entitled Agatha Christie: The ABC Murders. The game has players control Captain Hastings and must solve the mystery by inspecting crime scenes and questioning suspects. To appeal to players familiar with the original story, the game also offers the option to play with a different murderer, which results in different clues and testimony throughout the entire game. The game received mediocre reviews, but was commended for its faithful recreation of the source material.1936, Collins Crime Club (London), 6 January 1936, Hardcover, 256 pp
1936, Dodd Mead and Company (New York), 14 February 1936, Hardcover, 306 pp
1941, Pocket Books (New York), Paperback, (Pocket number 88)
1948, Penguin Books, Paperback, (Penguin number 683), 224 pp
1958, Pan Books, Paperback (Great Pan 95), 191 pp
1962, Fontana Books (Imprint of HarperCollins), Paperback, 192 pp
1976, Greenway edition of collected works (William Collins), Hardcover, 251 pp; ISBN 0-00-231014-7
1978, Greenway edition of collected works (Dodd Mead), Hardcover, 251 pp
1979, Pan Books, Paperback, 191 pp
1980, Collins Crime Club (London), Golden Jubilee of Crime Club with introduction by Julian Symons, Hardcover, 224 pp; ISBN 0-00-231323-5
1980, Ulverscroft Large-print edition, Hardback; ISBN 0-7089-0590-0
2006, Poirot Facsimile Edition (Facsimile of 1936 UK First Edition), HarperCollins, 4 September 2006, Hardcover; ISBN 0-00-723443-0
The first true publication of The A.B.C. Murders occurred in the US with an abridged version appearing in the November 1935 (Volume XCIX, Number 5) issue of Cosmopolitan magazine with illustrations by Frederic Mizen.
The UK serialisation was in sixteen parts in the Daily Express from Monday, 28 November to Thursday, 12 December 1935. All the instalments carried an illustration by Steven Spurrier. This version did not contain any chapter divisions and totally omitted the foreword as well as chapters twenty-six, thirty-two and thirty-five. In addition most of chapters seven and twenty were missing. Combined with other abridgements, this serialisation omitted almost 40% of the text of the published novel.