Ernestine Grant

In the short story The Third Floor Flat, Mrs Ernestine Grant was a young woman of about thirty five and the tenant of the flat on the third floor of the building Poirot was living in. Some eight years before the events in the story, she had married Donovan Bailey while in Switzerland. Subsequently Donovan became interested in Patricia Garnett, a woman who lived in the flat above Ernestine. Poirot speculated that Donovan must have tried to convince Ernestine that there was a flaw in the marriage. Ernestine had written to her solicitors and secured confirmation that her marriage was valid. Donovan shot her and contrived to steal the correspondence and marriage certificate.

Portrayals
Ernestine Grant was played by Josie Lawrence in the film adaptation of The Third Floor Flat in Series 3 of ITV's Agatha Christie's Poirot. She was depicted as having moved in to the flat the same day she was murdered. It was suggested that she had deliberately moved into the building (set in Whitehaven Mansions) in order to "hound" Patricia. In the original, Poirot thought it was merely a strange irony that both women ended up living one above the other. Her maiden name is given as "Ernestine Trapshaw".