Hercule Poirot is an elderly Belgian detective famous for his distinctive mustache and high self-regard. He relies entirely on his understanding of human psychology and logical deduction rather than physical evidence or action sequences. He travels to Woodleigh Common to investigate a local drowning, firmly believing the crime stems from a straightforward, logical motive rather than random madness. He prefers patent leather shoes over comfortable country footwear, prioritizing his appearance regardless of physical discomfort.

Ariadne Oliver is a successful mystery novelist who acts as a touchstone for the detective genre within the story. She possesses a somewhat scattered mind but immediately recognizes that the violence at the party connects to a hidden, logical motive. She famously loves apples, a preference that the local teenagers know from her television interviews, though the drowning incident quickly ruins her appetite for the fruit.

Miranda Butler is a quiet, nature-loving girl who frequently wanders through Quarry Wood. She stays home sick during the Hallowe'en party, missing the events entirely. She displays an unworldly innocence, quotes biblical scripture, and holds an intense appreciation for the natural world.

Joyce Reynolds is a thirteen-year-old girl known throughout Woodleigh Common for telling outlandish lies to gain attention. She dies violently during the Hallowe'en party, drowned in a bucket used for bobbing for apples. Her reputation as a storyteller causes the local villagers to completely dismiss her initial claim of witnessing a crime.

Rowena Drake is an authoritative widow who frequently oversees local community events. She inherited a significant fortune from her aunt, Mrs. Llewellyn-Smythe, following her husband's death in a car accident. She openly advocates for compassionate, remedial treatment for young offenders rather than harsh punishment.

Michael Garfield is a highly skilled gardener who originally worked for Mrs. Llewellyn-Smythe. He feels driven by a restless desire for artistic freedom and harbors an intense fixation on cultivating wild beauty. He dreams of purchasing a remote Greek island to design his ultimate, uninhibited landscape.

Judith Butler is a widow who works part-time to support her daughter, Miranda. She met Mrs. Oliver during a trip to Greece, where she helped the author out of the water after a boating accident. She worries extensively about modern social problems and the negative influences teenagers face.

Superintendent Spence is a retired police inspector living with his sister in Woodleigh Common. He offers Poirot valuable insights into the local residents and compiles a list of past, unusual deaths in the area. He possesses a paternalistic view of society, often expressing concern over decreased social oversight.

Elspeth McKay is Superintendent Spence's sister and housemate. She provides Poirot with practical information about the town's history and agrees with the general consensus that Joyce was a habitual liar.

Mrs. Reynolds is Joyce's distressed mother, who dropped her children off at the party but did not attend herself. She firmly believes Joyce fabricated the story about seeing a crime and assumes a male stranger must be responsible for the attack.

Ann Reynolds is Joyce's sixteen-year-old sister. She views Joyce as foolish and acts with a sense of superiority, agreeing with others that Joyce possessed no real enemies.

Leopold Reynolds is Joyce's clever, eleven-year-old brother. He calls his sister stupid and openly dismisses her boasts, demonstrating a calculating, unsentimental perspective on the family tragedy.

Miss Emlyn is the observant headmistress of the local school. She acts as a sharp assessor of character, easily separating trustworthy students from deceitful ones, and holds a pragmatic view of village life.

Elizabeth Whittaker is a teacher who attended the party to help chaperone. She provides a key operational detail to Poirot, noting a specific moment when Mrs. Drake unexpectedly dropped a heavy vase of water during the final game.

Nicholas Ransom is an adolescent boy who helped arrange the party games. He possesses a confident demeanor and freely offers wild, psychological theories about the local residents' motives.

Desmond Holland is a local teenager who created "spirit photographs" for the girls' party games. He applies a slightly more scientific or religious lens to his theories about the crime than his friend does.

Mrs. Goodbody is a local woman who played a witch at the Hallowe'en party. She relies on traditional nursery rhymes and religious explanations for evil, quickly dismissing modern psychological theories.

Jeremy Fullerton is a strict, rule-abiding solicitor who handled Mrs. Llewellyn-Smythe's affairs. He remains skeptical that the historical crimes in the village have any connection to the current drowning.

Mrs. Llewellyn-Smythe is Rowena Drake's wealthy, deceased aunt. She commissioned the elaborate Quarry Garden and left behind a complicated, contested will that sparks ongoing rumors in Woodleigh Common.

Olga Seminoff is a former au pair who worked for Mrs. Llewellyn-Smythe. She vanished entirely after producing a contested codicil that named her as the sole heir to her late employer's massive estate.