The ABC murders (1936) - featuring Hercule Poirot and written by Agatha Christie

Agatha Christie did a lot of experimentation with her books, sometimes confusing her readers by laying red herrings in some of her books that would mislead the users, in another she finally made almost all the characters in the novels as the guilty parties, and so on. In 'The Murder of Roger Ackroyd', she experimented with changing the narrator, and tried having the murderer be the narrator, and so on. In The ABC Murders, Christie experimented with having a mix of first person and third person narration (with Hastings trying to also reconstruct the third-person narrative).
Why is this book called The ABC Murders ? Well, because a series of murders is committed with the first person being killed having his name starting with 'A', the second with 'B', and so on. And each time, a letter (a challenge) is being sent to Hercule Poirot and the police before each murder, detailing where the murder will happen, but they are unable to prevent the murders from happening.



However, after 3 murders, there may be a break. The apparent 4th murder ('D') goes wrong, and then a man named Alexander Bonaparte Cust (ABC), who is a stocking salesman, walks in and confesses to the murders (he suffers from epilepsy, has blackouts, and has been near the scene of each of the murders and finds blood on his short cuffs), and the letter have been typed on his typewriter. And the clues that the police have found till now lead them to believe that the man committing the murder is a stocking salesman. But, there is a problem. He has not heard of Hercule Poirot (the wound to the pride of Poirot), and also does not have any idea about the letters. Poirot can soon prove that he has an alibi at the time of the murders and could not be involved.
And then it turns out that the murders are a blind, that innocent people lost their lives because one of the murders was desired for a specific financial purpose, and that the others were just done to set a different pattern. And this was the master planner, who had hired Cust to be near the scene of each crime as a part of each job, had used his typewriter to do the letters, and also put the blood on the cuffs.