In the short story The Horses of Diomedes, Sheila Grant is a young girl who is one of the "wild horses" which Poirot sought to tame in this particular labour of Hercules. Sheila attended a wild party at the house of Patience Grace where alcohol and drugs were freely available. Dr Michael Stoddart, who had been called there to attend to the victim of a shooting, found Sheila unconscious from the effects of cocaine. He was interested in the girl, having met her earlier at a hunt ball in Mertonshire. As such, he called Hercule Poirot to help rather than notify the police.
As Poirot would learn from his hostess in Mertonshire, Lady Carmichael, Sheila was one of four girls, daughters of one General Grant, a retired soldier from India who lived at Ashley Lodge nearby. All four girls were rather "wild" and had fallen among bad company, drinking and taking drugs.
However, Poirot recognised Sheila from a police photograph and discovered that "Grant" was a false name. She was actually Sheila Kelly, a shoplifter who had been sent to a reformatory some years before. On coming out, she had been approached by the man calling himself "General Grant" and offered a "post" as his daughter, with three other girls with the job of introducing drugs to their friends. Poirot confronted Sheila and urged her to give evidence to convict General Grant who was the centre of the drug ring. Poirot and Dr Stoddart would help her start afresh. Poirot later told Stoddart that if anyone could "tame" Sheila, he could.