Agatha Christie's intimate knowledge of chemicals found its way into her detective stories begining with her first mystery story. It was while she worked in the hospital pharmacy as a dispenser that she wrote her first novel. After finishing her chore of filling all the stock bottles, Christie used the slack time to work on a detective story in which the victim would be poisoned.
At her mother's encouragement, Christie used her two week vacation to finish her novel, The Mysterious Affair at Styles, at a nearby hotel in the moors of Dartmoor. As told by Mark Campbell in his book, The Pocket Essential Guide
, "In the summer of 1916 she booked herself into the 'large, dreary' Moorland Hotel, a few hundred yards from the summit of Haytor, to finish work on what would be the first of her 74 novels, The Mysterious Affair At Styles. In her autobiography she describes how she would write all morning, have dinner, wander alone across the moorland and re-enact out loud the chapter she was working on. Then she would come back, have dinner, sleep for 12 hours, and wake up and write passionately again the next morning."
Monsieur Hercule Poirot, the detective in Agatha Christie's first story, would not be an Englishman, but a diminutive foreigner who, although intelligent, would present a slightly bizarre figure. Retired from the Belgian police, Poirot was a plump elderly man, short -- barely 5 feet, four inches, with a balding, egg-shaped head, intelligent green eyes, and mustaches curling upward. His attire was impeccable and most always formal, if dated. Although often painful, his feet were typically shod in pointed black shoes and white spats.
Also appearing in The Mysterious Affair at Styles along with the fastidious Hercule Poirot is Captain Arthur Hastings, who would be his Watson-like companion in a series of stories and Inspector Japp of New Scotland Yard. In this first case of Poirot's, a country house matron is found in her locked bedroom dead of poison. The reader is presented with a wide range of clues, red herrings, and multiple subplots.
Of course, using his "little gray cells, the case is solved by Poirot, who will be less concerned with material clues than with the logic of the crime, specifically, untangling answers from a mass of contradictory data.