Third Girl
Agatha Christie
 Poirot's acquaintance, the mystery writer Ariadne Oliver, provides him with a number of key clues in the novel, beginning with the identity of the girl, Norma Restarick, whom she had met at a party. Mrs. Oliver and Poirot begin to investigate Norma, but soon find that she has apparently gone missing. Mrs. Oliver meets the girls with whom she shares a flat at 67 Borodene Mansions: Claudia Reece-Holland (who turns out to be secretary to Norma's father) and Frances Cary, an artsy girl with long, dark hair that falls across her face. Neither has seen Norma recently. Poirot (visiting her paternal great uncle’s home in Long Basing) finds that her father and stepmother also have no idea where she has gone. Poirot does meet David Baker, Norma’s boyfriend, in the house, and sees that Norma’s stepmother, Mary, is highly annoyed to discover him there. Poirot also meets Norma’s paternal great-uncle, Sir Roderick Horsfield, who is elderly and has poor eyesight. Norma’s father, Andrew, has been staying with Sir Roderick since returning from Africa, where he had made a vast fortune. Mrs. Oliver provides a second essential clue when she happens across David and Norma in a café. She telephones Poirot, who comes to meet Norma, while she herself tracks David to a dingy artist’s studio, where Norma’s flatmate Frances is posing as a model. Leaving the studio Mrs. Oliver is knocked unconscious. Meanwhile, Norma awakens to find herself in the safe keeping of Stillingfleet, having apparently thrown herself under an oncoming car. In a red herring that is easily spotted by those who recognise the doctor from an earlier meeting with Poirot, it seems that Stillingfleet may have kidnapped Norma. In fact, Poirot has hidden her from danger, and she is not seen again for much of the novel. Andrew Restarick employs Poirot to track her down, and is insistent that the police are not to become involved. Sir Roderick also contacts Poirot seeking help. He has lost letters written during the Second World War by a third party, which would now cause embarrassment should they be made public. Poirot’s attention attaches itself to Sir Roderick’s personal assistant, Sonia, who has apparently been passing secrets to a representative of the Herzogovinian Embassy at Kew Gardens. This is all a red herring, however: Poirot hints to Sonia that he knows of her espionage activities, and she abandons them in order to marry Sir Roderick instead at the end of the novel. Mrs. Oliver now provides Poirot with another key clue: she has heard while at Borodene Mansions that a woman has committed suicide by throwing herself out of the window of Flat 76. This, Poirot infers, must be the murder that Norma believed herself to have committed. Investigating the dead woman, he discovers that her real name was Louise Carpenter: also the name of a woman with whom Andrew Restarick had been in love many years earlier. Mrs. Oliver later even provides Poirot with the draft of a letter from Louise to Andrew in which she attempted to make contact once more: an item that had providentially come into her possession early in the novel when it fell from a drawer. Amongst other clues on which Poirot focuses, there are several that are only explained at the end of the book. Mary Restarick wears a wig, to which the reader’s attention is repeatedly drawn by the fact that Mrs. Oliver’s hairpieces are often mentioned as a plot device: indeed, Mrs. Oliver alters her hair in order to be in disguise when she sees Norma and David in the café. Also, Poirot notices that there is a pair of portraits of Andrew Restarick and of his first wife (Norma’s mother) in their home; why is Mary Restarick apparently content to have a picture of her predecessor on display, and why does Andrew later split the set in order to have his own portrait in his office? Stillingfleet contacts Poirot to say that Norma has walked out on him unexpectedly. She has seen a message in the personal column of a newspaper calling her to the flat, where she is discovered by Frances Cary standing over the dead body of David Baker with a knife, the murder weapon, in her hand. Norma immediately claims responsibility for the murder to a neighbour, Miss Jacobs. Norma has, however, been subjected to a cocktail of drugs intended to disorient her and make her susceptible to the suggestion that she is a murderer. In the denouement Poirot reveals that the man posing as Andrew Restarick is an impostor, Robert Orwell, who has taken his place after the real Restarick died in Africa. Orwell has persuaded David Baker to paint a fake painting in style with the original one, which establishes to anyone who questions it that the new “Restarick” had looked much the same fifteen years earlier when the pair was painted. Mary Restarick, meanwhile, has been leading a double life, as both Mary and as Frances Cary, whom she could become by changing wigs. Their imposture, however, could be revealed by two people: by David Baker, who had taken to blackmailing Orwell over the picture; and Louise Carpenter, who knew Restarick too well to be fooled by Orwell. The murder plot involved killing both of them, and convincing Norma that she was the killer. Norma had never in reality been in Louise’s flat: they simply switched the 7 and the 6 on the door of her own flat. All along the “third girl” in the flat on whom attention should have been focused has been, not Norma, but Frances. At the end of the novel, Stillingfleet, who has staunchly defended Norma’s innocence even when it was most in question, is rewarded by her agreeing to marry him. As Mrs. Oliver realises, Poirot has planned this happy ending all along.