What is the name of the first Hercule Poirot novel?

The Mysterious Affair at Styles is the first Hercule Poirot novel, written by Agatha Christie.

Christie wrote much of the book in 1916 during the First World War, and it was published in the United States in October 1920 before its British release in January 1921. The story introduces Poirot as a Belgian refugee living in England, along with his friend and narrator, Arthur Hastings, and Scotland Yard’s Inspector Japp.

The mystery takes place at Styles Court, where the wealthy Emily Inglethorp is poisoned. The country-house setting, concealed motives, red herrings, maps, and final logical explanation helped establish patterns that became closely associated with Golden Age detective fiction. The novel is sometimes confused with later Christie classics such as The ABC Murders or Death on the Nile, but those are separate Poirot adventures. Its sequel was The Murder on the Links.