Hercule Poirot is the protagonist of Hallowe’en Party and one of the novel’s third-person point of view narrators. Poirot, an elderly Belgian detective, appears in numerous Agatha Christie novels. In Hallowe’en Party, Poirot is brought on to the case of Joyce Reynolds’s murder by his longtime friend and mystery writer Ariadne Oliver.

Poirot’s character remains static throughout the novel, framed as someone who changes the narrative, not as someone who is changed by the events in the narrative. He employs a slow detecting style that depends on thinking and speaking to multiple witnesses, rather than engaging in high-action investigation, pointing to the text’s thematic interest in The Value of Community Knowledge. Indeed, Poirot complains of sore feet after a day of walking around Woodleigh Common, something that Mrs. Oliver attributes to his (in her view, foolish) insistence on wearing fancy patent leather shoes instead of more comfortable shoes better suited for the countryside. This choice, which Poirot refuses to give up no matter his physical discomfort, indicates Poirot’s vanity. He feels proud of his mustache, dyes his hair to avoid grays, and preens whenever he receives compliments on these things.