A mystery novel with a final body count of five might sound like a dark read, and yet the tone of Death on the Nile is surprisingly light. There are many funny moments bolstered by irony of all kinds. The third-person narrator has some distance from the events of the novel and is able to tell the reader about things unknown to the characters, including Poirot. The narrator relays things matter-of-factly, focusing on clues and character psychologies rather than digressions and intricate descriptions. Poirot does the same thing and often serves as a narrator proxy, but unlike the third-person narrator, he connects clues and creates hypotheses. Poirot's personality contributes to the light tone. He is not quick to either condescend or judge, and he has sympathy even for the criminals he apprehends.
The book also has a moralistic or cautionary tone: Poirot tries to give advice to Linnet and Jackie alike, and he also tries to impress upon Colonel Race the importance of expecting the unexpected. Poirot's moral lessons are fairly straightforward: for instance, he advises Linnet not to take from others less fortunate than herself, and he begs Jackie to resist "evil." Of course, neither character does as he asks, and the consequences are dire. Other moral judgements in the book are delivered through the ensemble cast and their behavior, both good and bad. Both the third-person narrator and Poirot think highly of Cornelia, for instance, while no one likes Mrs. Otterbourne's ego or alcoholism. Louise's death is especially cautionary: because she opted to blackmail Linnet's murderers rather than turn them in, she was also killed.