The Mysterious Affair at Styles, written by Agatha Christie in 1920, is the first of her novels to feature Hercule Poirot. The small, fastidious Belgian is one of her most iconic characters and among the most famous fictional detectives in the world. The novel is exemplary of the “cozy mystery,” in which well-heeled figures work out the solutions to complex, puzzle-like murders within comfortable settings. This one takes place during the years of the Great War, or World War I, on a secluded estate.

This summary refers to the Vintage Paperback edition, published in 2020.

Plot Summary

Note: This Plot Summary for The Mysterious Affair at Styles will reorder the book from the perspective of the murderer. Anyone wishing to experience the mystery and organization of Christie’s original plot should skip ahead to the chapter summaries.

In the midst of World War I, the widow Emily Cavendish marries Alfred Inglethorp, the secretary in charge of much of her wartime charitable work. Her first husband died many years ago, leaving the estate of Styles Court and all of his considerable money to his wife to do with as she wished. Emily Inglethorp is an inconsistent holder of said property, however, prone to often rewriting her will. Her stepsons, John and Lawrence Cavendish, have traditionally stood to gain the most from her inheritance, but the addition of Alfred Inglethorp has upended their expectations.

Almost instantly, the perfidious Alfred Inglethorp hatches a plan to murder his wife and take her fortune. He collaborates with one of Emily’s closest associates, Evelyn Howard. Together, they plan to introduce strychnine into her usual medicine, knowing that, due to a specific chemical reaction, the poison will not take effect until the last, crystallized drop of strychnine has settled to the bottom of the mixture and is swallowed. In order to redirect suspicion, they concoct a bizarre scheme to throw suspicion onto John Cavendish, falsely linking the purchase of strychnine to the step-son’s handwriting and arranging for him to be in a remote location free of alibis when the deed is done. On the night the last swallow is to be taken, Alfred cuts the cord to Emily’s service bell and waits remotely for the murder to happen.

Several circumstances complicate the plan. First, John invites his old friend Arthur Hastings to come stay at Styles; Arthur’s curiosity and connections will prove to be a vexing problem for Alfred and Evelyn. Emily forgets to take her medicine. Upset at the false letter’s suggestion that her stepson is having an affair, Emily cuts him out of her will. However, while looking for a stamp with which to send the updated will to her lawyer, she comes across a half-finished letter from Alfred to Evelyn, alluding to their dastardly plan. Emily hastily burns the will and spends a restless and well-founded evening fearing for her life.

The next day, Alfred leaves the estate, assured that Emily will take her medicine and die. Emily receives a late-night coffee but spills it on the floor, leaving behind a false clue. She consumes cocoa, and, unfortunately, her fatal dose of bromide. Unbeknownst to Alfred, Mary, John’s jealous wife, had earlier drugged Emily’s cocoa with a harmless sleeping powder to break into Emily’s room and steal the letter incriminating John. Emily begins her death throes with a frightened Mary still in the room. Mary hastily escapes, leaving a variety of false clues behind. Worse, Lawrence complicates things by hiding evidence which might incriminate Cynthia, the young woman staying in the bedroom next to Emily’s.

The next day, the family is eager to blame Alfred for the murder but can find nothing to link him to the crime. Evelyn too makes a show of blaming the murder on Alfred. She wants him to stand trial for the murder because he has an airtight alibi, which will absolve him of any future prosecution. Arthur immediately recruits his friend Hercule Poirot to investigate. Poirot, a Belgian war refugee and former detective, is staying in the nearby town due to the charity of Emily Inglethorp. He is eager to engage his famously sharp mind in her service. He inspects the room and then immediately commands that it stay locked. Alfred is never alone in the room long enough to hide the letter Emily had found about him and Evelyn. Instead, he hastily rips this letter in three and twists the pieces, placing them above the fireplace to be used as starter wicks.

Poirot sorts through the clues, expertly eliminating one red herring after another. At an inquest against Alfred, a suspicious Poirot quickly produces Alfred’s alibis, in an effort to stave off a too-hasty trial. Only after John Cavendish is brought in based on Alfred and Evelyn’s manufactured evidence does Poirot reveal all he knows, including the torn letter above the mantelpiece. The true criminals are arrested, and everyone is astonished by Poirot’s skills. Alfred and Evelyn are arrested, and many of the Cavendishes become closer as a family due to their ordeal.