Curtain is a Hercule Poirot mystery novel by the best-selling author Agatha Christie. The story follows the main character, Arthur Hastings, where he embarks on a trip to stay in the Styles guesthouse, which is a house that he once lived in when his friends owned it. Hastings meets his good friend, and famous investigator, Hercule Poirot, who is also staying the Styles guesthouse. Hercule Poirot is a French private investigator that is world renown for solving some of the most perplexing mysteries. When Hastings arrives at the guesthouse, Poirot shows Hastings a paper that describes five different murder cases. Poirot tells Hastings that the murderer, which he names X, is responsible for all five cases.

Poirot says he knows who the killer is but he doesn't know who the intended victim is. Poirot also tells Hastings that he won't reveal to Hastings who X is. Poirot is also very old and has a bad heart. He has just returned from Egypt and so he is in a wheelchair. Poirot tells Hastings that because his mind is able but his body isn't, Poirot needs Hastings to help him with the investigation.

When Mrs. Franklin, the wife of the doctor and Hastings daughter's boss, Dr. Franklin is poisoned, it appears as if X has struck again. While the death is rendered a suicide, Poirot emphatically tells Hastings that she was purposely murdered.

By the end of the novel, Norton, another of the houseguests and who Poirot determines is X, is dead by Poirot's hand. Poirot has also died of what the coroner says is a heart attack.