She wrote her first novel as a dare.

Christie's sister Madge issued a challenge to her siblings to tackle a novel-length project following adolescence spent reading and creating short stories. In response to the challenge, Christie created The Mysterious Affair at Styles, a suspenseful novel about a sick soldier who becomes involved in a poisoning event at a friend's compound.

In addition to reading early Sherlock Holmes tales by Arthur Conan Doyle and Wilkie Collins, Christie has long been a devotee of detective fiction. The Mysterious Affair at Styles, her debut detective book, was written by her in 1916. Hercule Poirot, a former Belgian police officer with a "lovely mustache" and "similar fruit" "head eggs," was depicted. After the German invasion of Belgium, Poirot fled to England.

Belgian refugees who settled in Torquay and the Belgian soldiers she assisted in treating as a volunteer nurse during World War I served as Christie's inspiration for the character. Hodder & Stoughton and Methuen turned down her initial manuscript. John Lane at The Bodley Head offered to accept the report after holding onto it for a while, but only if Christie altered how the solution was revealed. She did so and executed a contract, which she later thought was exploitation, committing her following five works to The Bodley Head. Before being published in 1920, the Hercule Poirot novel was rejected by six publishers