Wasps' Nest - S3-E5
Plot hole: There are some additions to the original short story in this dramatization, but they create a little problem since Hastings does not come with Poirot for the finale, and in fact is told to stay home in a rather demeaning way. Without Hastings, it's hard to imagine Poirot could break into Langdon's house, since Capaldi when is not playing creepy clown is a sculptor working at home; Poirot would need an accomplice to create a diversion. And, even sillier, Poirot tells Hastings to go buy him some washing soda, but he needs the soda to pull off the switch. Hastings should have joined him at least to give him the soda once Poirot has visited the doctor.
Wasps' Nest - S3-E5
Factual error: When we see the cover of Vogue magazine where Molly Deane appears, the recreation is not bad (the lettering used is not a classic Vogue one but something very similar was used for instance in August of the same year as portrayed), but the bar at the bottom gets the date wrong, putting it down as September 10th 1935, when Vogue always had 1st and 15th of the month as date of the release, no matter the day of the week. Also, it completely omits for instance the price. Would be a pretty difficult magazine to sell without that, real Vogue covers have that detail prominently displayed. (00:03:20)
Wasps' Nest - S3-E5
Continuity mistake: Poirot is examining the photos taken by Hastings at the party. Depending on the camera angle, the pictures and their reciprocal distance change across the whole sequence. (00:15:30 - 00:16:05)
Wasps' Nest - S3-E5
Continuity mistake: Having received Japp's phone call, Poirot puts down the picture of the mysterious man. The photo sits on top of the other pictures in a different spot at the cut. (00:35:35)
Wasps' Nest - S3-E5
Factual error: When John Harrison check out of the organizer, the days of the week are wrong for a 1935 setting (September 24th is a Monday, etc), looks like a 1934 one. (00:12:00)