The Adventure of "The Western Star"by Agatha Christie is a Poirot short story published 11 April 1923
Poirot receives a visit from Miss Mary Marvell, the famous American film star on her visit to London. She has received three letters, handed to her by a Chinese man, which warn her to return her fabulous diamond jewel, the "Western Star", to where it came from – the left eye of an idol, before the next full moon. Her husband, Gregory Rolf, who bought it from a Chinese man in San Francisco, gave Mary the jewel three years ago. The pair are going to stay at Yardly Chase, the home of Lord and Lady Yardly when the moon is next full to discuss the making of a film there and Mary is determined to go with her diamond. Both Poirot and Hastings remember society gossip from three years back that linked Rolf and Lady Yardly.