I think the director should take credit for the pacing and how well constructed the episode is even though the initial story might be a bit slight. From the flashbacks to a duel, trying to keep you guessing who the murderer is by trying to hide scarface, then leaving the viewer to contemplate that this was a really gruesome murder.
Poirot is approached by Lady Chatterton who was a suspect in an earlier case and she tells him that she thinks her friend Marguerite Clayton (Caroline Langrishe) is in danger from her husband. Mrs Clayton is a great beauty who had many admirers and Lady Chatterton could not understand why she married a man like him.
Poirot attends a party so he can observe Mr Clayton but he never shows up. Inspector Japp turns up the next day to inform Poirot that he might had been a witness to his murder. His body was contained in a Spanish chest on the evening of the party.
Major Rich is arrested, a man recently widowed and who has spent a lot of time with Marguerite.
An enjoyable episode even though it is easy to figure who the charmless culprit is. A bonus is that you get to see Poirot doing the Charleston.