Miss Marks

In the short story The Cornish Mystery, Miss Marks was the attractive young clinical assistant of Edward Pengelley, a dentist in the Cornish town of Porgarwith. Edward's wife, Mrs Pengelley called her a "yellow-haired hussy" and suspected that her husband was attracted to her.

After Mrs Pengelley died, Edward Pengelley announced his engagement to Miss Marks. Popular sentiment, the "voice of the people" or "vox populi" soon resulted in a petition being sent to the Home Secretary. The body of Mrs Pengelley was exhumed and found to have large quantities of arsenic. Edward was arrested and tried for murder. During his trial, Miss Marks wept and "went into hysterics". She admitted that there had been "passages" her and Edward and that he had promised to marry her if his wife died.

Portrayals
Miss Marks was played by Laura Girling in the film adaptation of the story in episode 4 of Series 2 of ITV's Agatha Christie's Poirot drama series. The credits list her name as "Edwina Marks". This firstname is not found in the original story nor does it occur in the episode dialogue. Her portrayal is fairly faithful to the original story. There are some additional scenes, one where Hastings is tongue-tied when encountering her for the first time and another when Japp is arresting Edward. She runs after them protesting that Edward is innocent. Her testimony during the trial is not depicted in the episode.