The "Western Star" of the title is a flawless diamond that supposedly represents one eye of a Chinese god; the other eye is represented by an equally valuable diamond, the "Eastern Star". The first is owned by a Belgian female film star and her husband; the second by an English Lord and his wife. When both couples receive anonymous letters threatening them that their diamonds will soon be stolen, Hercule Poirot comes to the rescue.
This is one of the tightest, most story-driven "Poirot" episodes I've seen so far. Usually there's some sightseeing or some subplot along the way, but this time almost every one of the 50 minutes is, directly or indirectly, related to the main plot. Another notable thing is that one big twist is revealed halfway through - and the story just keeps going. Hugh Fraser has some outstanding acting moments in this one, particularly when Captain Hastings THINKS he knows what's going on. Well worth seeing. (***)