Hercule Poirot met his lifelong friend, Captain Arthur Hastings, and solved the first of his cases to be published, "The Mysterious Affair at Styles". It is clear that Hastings and Poirot are already friends when they meet in Chapter 2 of the novel, as Hastings tells Cynthia that he has not seen him for "some years". Particulars such as the date of 1916 for the case and that Hastings had met Poirot in Belgium, are given in "Curtain: Poirot's Last Case", Chapter 1. After that case, Poirot apparently came to the attention of the British secret service and undertook cases for the
Hercule Poirot partly because there is rarely a narrator to mislead. In "Murder on the Links," still largely dependent on clues himself, Poirot mocks a rival "bloodhound" detective who focuses on the traditional trail of clues established in detective fiction (e.g., Sherlock Holmes depending on footprints, fingerprints, and cigar ash). From this point on, Poirot establishes his psychological bona fides. Rather than painstakingly examining crime scenes, he enquires into the nature of the victim or the psychology of the murderer. He predicates his actions in the later novels on his underlying assumption that particular crimes are committed by particular types of people.