A wealthy, sharp-tongued spinster named Emily Arundell rules her family from her house in the quiet market town of Market Basing, where her relatives circle in hope of inheriting her considerable fortune. After a near-fatal tumble down the stairs, apparently caused by a ball left by her wire-haired terrier Bob, she comes to suspect the fall was no accident at all. Quietly alarmed, she writes a cautious letter to Hercule Poirot, hinting at her fears without naming the danger, and posts it. The letter takes weeks to reach him, and by the time Poirot and Captain Hastings travel down to investigate, Emily is already dead, her passing attributed to a long-standing illness. Convinced that the delayed plea points to murder, Poirot sets about reconstructing the events around the old woman's last days, sifting through the greedy ambitions, money troubles, and tangled loyalties of her heirs. The only true witness to what happened on the stairs cannot speak, and the household offers a thicket of motives and quiet evasions. Narrated by the genial, often baffled Hastings, the case turns on small domestic details, a contested will, and the patient logic of a detective who refuses to accept a convenient explanation. Poirot must coax the truth from the living when the dead can no longer testify, and decide whether an old woman's instinct was sound or merely the fancy of a frightened mind.