While most of Agatha Christie's stories feature murders, some stand out as especially heinous, plunging their perpetrators utterly beyond redemption. These include child murders, certain particularly cold-blooded murders that prey on the victim's innocence, and any murders falling under the Serial Killings, Specific Target and Trial Run Crime tropes.note
- The ABC Murders: The killing of people with alliterative names simply to disguise the identity of the intended target, whose name is alliterative, while making an innocent man think himself the Ax-Crazy perpetrator and trying to get him hanged for the killings.
- And Then There Were None: Has its own page.
- The Body in the Library: The murder of the Girl Guide to establish an alibi for the first murder.
- Curtain: The villain is on the other side of this before the novel begins, having psychologically manipulated numerous unhappy, desperate people into committing murders they wouldn't otherwise have done, simply for his own pleasure.
- Death Comes as the End: While the serial killer has a strong Freudian Excuse and initially targets Asshole Victims, he has definitely crossed this line by the time he has commanded his obedient, devoted slave boy to kill himself, after using him as a cat's paw.
- Destination Unknown: Thomas Betterton leapt over this by romancing, marrying and then murdering Elsa, all just so he could steal the credit for her brilliant scientific work.
- Evil Under the Sun:
- Patrick serially romancing, defrauding and murdering young, naive women for their money.
- Christine inducing young Linda to attempt suicide as a scapegoat.
- Hallowe'en Party: Michael Garfield grooming Miranda, his own innocent biological daughter, to be "sacrificed" and then attempting to carry it out on an altar, just because she could be a danger to his narcissistic desire to build a garden on a Greek island.
- Hickory Dickory Dock: The utter lack of remorse with which Nigel poisoned his kind mother and then bludgeoned his sort-of-girlfriend to death because of her writing a letter to his father hoping that they would reconcile.
- Murder in Mesopotamia: The second murder, due to how horrific and painful it is. Dr. Leidner kills Miss Johnson by substituting hydrochloric acid for her bedside drink, because she knows too much. When unmasked by Poirot, he acknowledges that he has crossed this line.
- Murder is Easy: The villain crosses this by killing seven people, some with very painful methods, for no other reason than to frame her ex-fiancé in revenge for him breaking off their engagement.
- Murder on the Orient Express: An exaggerated case. The kidnapping and murder of the baby Daisy Armstrong - even after the family had paid the ransom - puts the villain squarely in monster territory.
- The Pale Horse: The villain of the story, Zachariah Osbourne, runs a commercial criminal operation by serially murdering people using the slow and painful method of thallium poisoning.
- A Pocket Full of Rye: The use of Gladys as a cat's paw and then her murder when she had outlived her usefulness.
- Sleeping Murder: James Kennedy ruining Helen's entire life from start to finish through social isolation and Malicious Slander, before murdering her and gaslighting her husband Kelvin into believing he went insane and killed his own wife.
- Three Act Tragedy: The murder of Stephen Babbington as a casual dress rehearsal for the main murder.
- Towards Zero: The killer murders his own mother figure just for the opportunity to frame his ex-wife and have her hanged.
- Schaefer of "The Wife of the Kenite" crossed it several years before the story begins. The reason he recognises the woman and associates her with motherhood is because during the invasion of Belgium his regiment passed through her village and her four-year-old son was frightened. When he ignored Schaefer's order to stop crying, Schaefer chopped his hand off, laughed and joked about it, and then battered him to death against the wall.
