Nurse Harrison

In the short story The Lernean Hydra, Nurse Harrison is a nurse working in the village of Market Loughborough in Berkshire. She had worked as the nurse of the wife of Dr Charles Oldfield and had been in that post for some three years at the time of her death. She then moved on to work for Miss Bristow.

Poirot eventually unmasked Nurse Harrison as the murderer of Mrs Oldfield. She had been giving her patient arsenic which was discovered after the body of the dead woman was exhumed. Harrison was also responsible for starting the rumours that Dr Oldfield had poisoned his wife. The motive, Poirot surmised, was jealousy. Harrison, having worked with Dr Oldfield at close quarters for some three years, had formed the impression that the doctor loved her and would ask her to marry him after his ailing wife died. However, after murdering the wife, Harrison discovered that the doctor was interested in the younger Jean Moncrieffe instead. Her anger and jealousy then led her to spread the rumours about the doctor and Jean.

Nurse Harrison was described as "still a handsome woman nearing forty. She had the calm serene features of a Madonna with big sympathetic dark eyes."

"The pity of it," Poirot had said, when unmasking her as the killer. She would probably have made a good wife and mother but her emotions were just a little too strong for her.