What is the theme in Peril at End House, by Agatha Christie by Agatha Christie?

Deception is a central theme in the book. Peril at End House is filled with deception. The whole story as Poirot and Hastings see it is orchestrated by Nick Buckley, specifically to deceive. Nick engineers fake attempts on her life, and creates the illusion that she is engaged to Michael Seton. Nick is only able to do this because of another deception. Maggie Buckley and Michael Seton are deceiving Seton's uncle by keeping their marriage plans a secret. If it weren't for this deception, Nick would never be able to attempt her plan. Maggie believes that one should keep one's feelings to oneself, and not burden others with them, an attitude she expresses shortly before her death. By keeping her feelings about Michael Seton's disappearance inside, another kind of deception, she unwittingly makes Nick's plan possible.