A frail, wheelchair-bound Hercule Poirot returns to the site of his first case to prevent a final, calculated murder from occurring among a group of house guests. Poirot, physically diminished by age and illness, must rely on his intellect and the assistance of his long-time companion, Captain Hastings, to identify a serial killer hiding in plain sight. The narrative unfolds through the perspective of Hastings, who struggles to reconcile his friend's cryptic warnings with the seemingly benign behavior of the suspects. As the tension mounts within the confines of Styles, the duo faces the challenge of stopping a predator who operates with cold, psychological precision.

Curtain is widely regarded as a poignant and definitive conclusion to the Hercule Poirot series, noted for its departure from the traditional lighthearted tone of earlier mysteries. Critics and readers frequently highlight the emotional weight of seeing the iconic detective in his final days, struggling with his physical limitations while maintaining his mental acuity. The novel is often praised for its dark, introspective exploration of justice and the complex psychological profile of its antagonist. It remains a significant work in the detective genre, frequently cited for its bold narrative choices and its impact on the legacy of Agatha Christie's most famous character.