In the short story The Adventure of 'The Western Star', Lady Yardly, formerly Maude Stopperton, was the wife of Lord Yardly. Some three years before the events in the story, she had been seen going about with the actor Gregory B. Rolf during a visit to Hollywood. Lady Yardly later told Poirot that she had never been more than indiscreet. However Rolf had kept some letters of hers which he used to blackmail her. She had no money of her own to pay him, and she feared divorce, so instead she gave in to his demands. He demanded and received from her a fabulous diamond "The Star of the East" which had been in Lord Yardly's family for generations. Rolf had arranged for Lady Yardly to have an imitation made, but matters came to a head when, during the story, Lord Yardly wanted to sell the diamond to clear debts. She contacted Rolf, and since he stood to be expose if Lady Yardly decided to confess the whole story, he decide to help her by staging a robbery of both the paste stone and the real diamond, and hide the motive behind a smoke screen, by posing it as robberies committed by Chineses.
Poirot was able to restore the diamond to her at the end. Comparing the two women he had to deal with in the story, Poirot had greater sympathy for Lady Yardly than for Mary Marvell. To him, Lady Yardly was "Bonne mère, très femme!"
Lady Yardly was played by Caroline Goodall in the film adaptation of The Adventure of 'The Western Star' in Series 2 of ITV's Agatha Christie's Poirot. In the original, Lady Yardly had said that she had been recommended to Poirot by her friend Mary Cavendish. This reference is not mentioned in the adaptation, nor does Poirot make the remark of Lady Yardly being a good mother.