Nurse Harris is the murderer who appeared in The Labours of Hercules, a short story collection written by Agatha Christie and features Belgian detective Hercule Poirot. She appeared in the second story, The Lernaean Hydra. She only appeared in the novel and was not presented in the TV episode adaptation of the short story collection.
The Lernaean Hydra
The story begins when Poirot is asked for help by a physician, Dr. Charles Oldfield, who has a practice in Market Loughborough, a small village in Berkshire. His wife died just over a year ago and the malicious talk in the village is that he poisoned her. People are avoiding him and several poison pen letters have been sent to him but he can do nothing to stem this tide of ill-intentioned gossip – like the heads of the Hydra, when one source of the gossip is cut off, another grows in its place. So, his ultimate aim was to cut the main source of the gossip, just like the hydra had been slayed by cutting its vulnerable head.
Mrs. Oldfield was a difficult invalid whose death was put down to a gastric ulcer, whose symptoms are similar to that of arsenic poisoning. She left her husband a not-considerable sum of money and, under pressure, Oldfield admits that a lot of the talk revolves around Jean Moncrieffe, his young dispenser, who he wants to marry but dare not because of the talk. Poirot travels to Market Loughborough and meets Jean. She is frank about her relationship with Oldfield and her dislike of his wife but opposes Poirot's idea of an exhumation and autopsy on the body. Poirot makes the rounds of the village, insinuating that he is connected with the Home Office and thereby generating much hypocritical murmurs of sympathy for the doctor and, more importantly, names of who said what and when.
From this he learns of the present whereabouts of two servants of the Oldfields who left their employ after Mrs Oldfield died; Nurse Harrison, who tended to the patient, and Beatrice, the family maid. Nurse Harrison tells a story of overhearing Jean and the Doctor talking about the imminent death of his wife in which it was clear that this was an event that both of them were impatiently waiting for. The nurse is certain that Beatrice must have overheard the talk as well. Poirot tells her of the supposed plans of exhumation and the nurse considers this news and then tells him she agrees that such a thing should be done. While being interviewed, Beatrice slyly denies overhearing any conversation but tells him of several suspicious stories of Jean making medicines or pots of tea for Mrs Oldfield which the nurse poured away or changed before the patient could take them.
Poirot does indeed get permission for an exhumation and the body is proved to be riddled with arsenic. Nurse Harrison is shocked and tells Poirot a new story of seeing Jean filling up a make-up compact with a powder from the dispensary. Poirot alerts the police who find such a compact in the bureau of the bedroom of Jean's lodgings. They show it to Nurse Harrison who excitedly confirms that is the one she saw…only for Poirot to tell her that such compacts have only been manufactured for three months and that he had his valet, George, follow her some days previously, witnessing her purchase of a compact at Woolworths and then travelling to Jean's lodgings to secrete it there. Trapped and broken, Nurse Harrison admits the murder.
Poirot speaks with Jean and tells her that the conversation Nurse Harrison claimed to have overheard seemed psychologically unlikely as two possible conspirators would never had had such a conversation in a place where they could be easily listened to. He observed the nurse's positive reaction when he told her of a possible exhumation and then had her followed by George who witnessed the buying of the compact and the laying of the trap for Jean. The motive was jealousy as Nurse Harrison was convinced by Oldfield's kind manner over several years that he intended her to be his bride.