1936 novel by Agatha Christie, often considered to be one of her best works. Hercule Poirot has received a letter after retirement, daring him to solve a case before a victim for every letter of the alphabet is killed (and it's not a Spoiler Title).
This detective mystery provides examples of:
Alliterative Name: The victims of the killer: Alice Ascher, Betty Barnard and Sir Carmichael Clarke.
Calling Card: The murderer leaves a book of railway timetables at the scene of each murder. The book in question, naming all the stations in Britain in alphabetical order, is known as an ABC.
Chekhov's Gun: A rare case here, as while the Chekhov's Gun is not applicable in this book, it is relevant to a later Christie novel, Curtain. Within the opening pages of this novel, Hastings comments (once learning that Poirot dyes his hair) that the next time Hastings sees Poirot, he will be wearing a fake mustache. In Curtain, the last Poirot mystery, Poirot dons a false mustache, which becomes key to understanding the murder.
Gold Digger: Poirot suspects that Thora Grey is one, to Hastings's displeasure. This ends up being important to the motive of the murderer: If Thora had married Sir Clarke and perhaps had children, Franklin would not have inherited his brother's money.
Instant Death Knife: The fourth murder is committed in a cinema. The murderer leaves in the middle of the film, pretends to stumble, leans forward and stabs a random man, who dies instantly, without making a sound.
I Was Quite a Looker: When Poirot and Hastings see the dead body of the first victim, Alice Ascher, an elderly storekeeper, Poirot notes that she must have been beautiful when she was young. Hastings doubts it, but later, when they find her wedding photo, he sees that Poirot was right.
Murder by Mistake: Subverted. It appears to occur with the fourth murder, which does not fit the killer's pattern. In reality, the identity of the victim was unimportant to the pattern; the victim was simply chosen at random, on the assumption that someone who in factdidfit the pattern would be nearby.
Also exploited by the murderer for the fourth murder. The police know where and when it will be in advance, Doncaster, and that the target should be someone whose name starts with D, so they should be able to catch him...except that the date in question is that of the St Leger Stakes, one of the biggest horse racing events in England, so Doncaster is flooded with visitors from all over the country.
Never One Murder: Lampshaded at the beginning when Poirot and Hastings talk about murder mysteries, and Hastings says that it's good if a story has more than one murder, because otherwise it could get boring.