Arthur is a military veteran staying at the secluded Essex estate of Styles Court to recover from battle injuries. He fancies himself an amateur sleuth but frequently struggles to interpret clues accurately. He provides an honest, though often confused, perspective on the strange events at the estate, occasionally distracted by his romantic interest in the women around him.

Poirot is a short, exceptionally neat Belgian man with a distinctive egg-shaped head. A former notable detective in the Belgian police force, he now lives in Essex as a refugee due to the German invasion of his homeland. He relies on his "little grey cells" and methodical observation to bring order to chaotic situations, operating with a theatrical flair.

Emily is the wealthy, elderly matriarch of Styles Court. She controls her late husband's considerable estate, using her fortune and frequent will revisions to assert authority over her family. She heavily involves herself in local wartime charitable work, including sponsoring a local group of Belgian refugees.

Alfred is Emily's former secretary and newlywed husband, twenty years her junior. He possesses a distinctive look featuring dark clothing, a heavy black beard, and glasses. His sudden elevation to master of the house creates intense friction with his wife's family, who view him as an opportunistic outsider.

Evelyn is Emily Inglethorp's closest friend and practical, literal-minded secretary. She is fiercely protective of her employer and outspoken in her deep distrust of Alfred. Her aggressive opinions frequently create tension within the household.

John is the older stepson of Emily Inglethorp. He lives the life of an English country gentleman on an allowance from his stepmother. Though he wishes to project the legacy of the Cavendish name, he struggles with financial strain and a slowly deteriorating marriage.

Mary is John's intelligent and striking wife. She finds the secluded country life at Styles Court stifling and behaves with a cool detachment toward her family's drama. She maintains a keen interest in modern topics, including advanced poisons, and acts independently of her husband's wishes.

Lawrence is the younger Cavendish brother. He studied medicine but abandoned the field to pursue literature, to his family's dismay. He is generally quiet, reserved, and observant, relying on his stepmother's allowance to sustain his modest lifestyle.

Cynthia is a young woman living at Styles under Emily Inglethorp's charity after her own mother died. She works as a manager at a local Red Cross drug dispensary. Despite her cheerful exterior, she often feels out of place and beholden to her domineering benefactress.

Dr. Bauerstein is an esteemed toxicologist visiting the local town from London on holiday. He possesses highly specialized medical knowledge and maintains a regular presence around the estate, frequently walking or conversing with Mary Cavendish.

Dorcas is the loyal, long-serving maid at Styles Court. She is deeply devoted to Emily Inglethorp and meticulously observes the household's routines, later providing crucial details about schedules, missing items, and family arguments.

Japp is a pragmatic and efficient detective from London's Scotland Yard. He has a prior working history with Hercule Poirot and respects the Belgian detective's methods, though he prefers straightforward, physical evidence over psychological deductions.

Mrs. Raikes is a young, beautiful local farmer's wife. Her presence in the village generates considerable rumor and friction within Styles Court, particularly concerning the men of the Cavendish household.