Curtain by Agatha Christie

Hercule Poirot returns to Styles—the place where his first case began—but this time, it is for his final investigation. An elusive killer is orchestrating deaths from behind the scenes, manipulating others into committing murder without direct involvement. As Poirot’s health declines, he must solve one last, deeply personal case where the enemy is invisible, intelligent, and dangerously close. This novel delivers a powerful and emotional farewell to Christie’s most famous detective.