Poirot is a renowned detective characterized by his use of his "little grey cells" to solve complex mysteries. Despite being underestimated due to his appearance and accent, he gains the confidence of those around him.

Emily is a wealthy woman known for quickly changing her will to influence those around her. She invites Poirot to Styles Court, leading to his investigation of her murder.

Alfred is Emily’s husband, initially suspected due to his means and opportunity, and presents an unsettling demeanor. Evelyn Howard, Emily’s secretary and friend, provides strong support for Emily and is vocal against Alfred.

John is Emily's stepson, facing trial for her murder, and struggles with maintaining his family legacy. His wife, Mary, despite their strained relationship, becomes his key supporter.

Lawrence, John's brother, pursued medicine and briefly literature, while Cynthia volunteers in postwar work at Styles. Their shared knowledge of medicine becomes significant as they navigate suspicions and personal feelings.