Mary Marvell

In the short story The Adventure of 'The Western Star, Mary Marvell' was an American film star, according to Captain Hastings, probably one of the most popular actresses on the screen. While in London, she sought Poirot's help because she had received a series of blackmail letters. These told her that a fabulous diamond in her possession, "The Western Star", was the left eye of a Chinese idol. It should be returned, or else it would be taken from her on the night of the full moon. In spite of the danger, however, Mary refused to hand the jewel to Poirot for safekeeping as she and her husband, actor Gregory B. Rolf, planned to visit Lord Yardly at Yardly Chase and she wanted to wear her diamond there because Lady Maude Yardly was reputed to have another famous diamond, "The Star of the East".

Mary did not know that there was no such thing as "The Western Star". It was actually "The Star of the East" which Gregory Rolf had extracted from Lady Yardly by blackmail. Mary's letters and the subsequent theft of her diamond from her hotel safe was all part of an elaborate fraud scheme by Rolf.

Mary was described as "mall and slender, very fair and girlish-looking, with the wide innocent blue eyes of a child."

Hastings expressed sympathy for Mary Marvell at the end of the story. She had lost her diamond through no fault of her own. However Poirot was inclined to be dismissive. "She has a magnificent advertisement. That is all she cares for, that one!" He had greater sympathy for Lady Yardly whom he considered a good mother.

Portrayals
Mary Marvell was played by Rosalind Bennett in the film adaptation of The Adventure of 'The Western Star' in Series 2 of ITV's Agatha Christie's Poirot. There she is transformed from an American filmstar into a Belgian filmstar. Her name is tweaked slightly to the more French sounding "Marie Marvelle". In contrast to Mary Marvell in the original story, Poirot idolized Marie and it was a source of irritation to him that no one else seemed to think there were any filmstars from Belgium. He sympathised with Marie's plight and visited her at the end of the episode to break the bad news about her husband and her diamond. Hastings remarked at the end that all Poirot had achieved for Marie at the end was the loss of her husband. To this, Poirot replied that she had lost a husband who was an adulterer, a blackmailer and a thief. That was not such a bad thing to lose.