This is one of the more faithful story adaptations of the series. Poirot and Hastings are consulted by an actress who has received threatening letters regarding The Western Star, the large diamond given to her by her husband. Poirot offers to keep the diamond safe, but the actress wants to take it to Yardley Chase to show it off to Lady Yardley, who is said to have a large diamond of her own. The next day, while Poirot is out, Hastings is visited by Lady Yardley. Hastings tells Lady Yardley that he knows that she must have received letters as well, and agrees that he will go with Poirot to Yardley Chase that evening. But when they get there, as Lady Yardley is getting ready to show them the diamond, the lights go out, Lady Yardley screams, and the diamond disappears. Can Poirot discover who has the diamond, and get it back to its rightful owner?
Since it is a faithful rendering of the story, it comes off quite well. The extra details that have been added by the writers are mildly amusing, and don't take anything away from the story. The actress in this version is supposed to be Belgian, and there is a bit of a running joke about how Poirot seems to be the only man in England who is aware that there is such a thing as a Belgian film star. And Japp, who spends the episode trying to bring to justice the man who is trying to buy the stolen diamond, has the rug pulled out from under him yet again at the end. Overall, quite a good retelling of the story but nothing special.