What are the motifs in Peril at End House, by Agatha Christie by Agatha Christie?

Justice is a recurring idea. In the novel, Maggie Buckley's parents are the people who most need justice. They are the ones who have been wronged and have been robbed by Nick Buckley's actions. Maggie Buckley herself can no longer be helped, though Poirot does believe that the victim deserves justice through the punishment of the killer. Maggie's parents' presence in the novel is a strong motivator for Poirot to bring the crime home to its perpetrator.