Factual error: Poirot gets on the train to London. The engine has an SNCF plaque on it. The video then cuts to the 1936 cycle race. The BCNF was not formed until 1938.
Plot hole: When Poirot and Hastings break into the house, they search the entire house for the box, without success. However, later on, when they are in the kitchen, the housekeeper comes down the stairs - having been lying in wait for them. How did Poirot not run into her when he was initially searching upstairs, particularly when he was making such a thorough search?
The Tragedy at Marsdon Manor - S3-E6
Factual error: It is well established that the episode takes place in 1935 (Nairobi Daily Press dated Saturday July 27 1935, the poster in town advertises the meeting for "Today, Wednesday September 4th", day of the week consistent with the year), but Poirot and Hastings are stopped on their way to the train station by a Wolseley Series II - 14/56, a model that entered production in mid 1936. (00:17:00)
Factual error: At the party, Marcus Hardman tells Bernard that the Countess recently arrived from Russia, and she describes herself as being in exile. Which made sense in the source material, set right after the Russian Revolution, but less sense in this adaptation, set in the mid 1930s. If she stayed in Russia that long, she would have spent 15-20 years with zero privileges from her rank at that point, and nothing from her old wealth, seized by the communist government.
The Tragedy at Marsdon Manor - S3-E6
Other mistake: Investigating Poirot's investigation, the clumsy constable crushes a tiny egg under his foot. Poirot crawls to him and points with his cane at the other eggs in the bush. But he points practically at his shoe, and the eggs are in a different spot to the left. (00:20:10)
The Tragedy at Marsdon Manor - S3-E6
Plot hole: The murderer is in possession of chloroform from the doctor's cabinet, but there's no realistic timeframe when they could have done it, nor any explanation why the doctor notices it completely at random when Poirot visits, just approaching the medicine cabinet, something he routinely opens and looks through during the day.
Continuity mistake: The Countess arrives at the hotel at the beginning of the episode. In the overhead shot she reaches the top of the stairs with nobody close to her, just the porters behind her, but in the next shot there are other people in the lobby, who at the next cut are even closer to her to fit in frame. (00:02:10)
The Tragedy at Marsdon Manor - S3-E6
Plot hole: The murderer planned everything making it seems accidental. They perfectly managed to fool the coroner and need only to be alone at the mansion to get rid of the murder weapon. So what they do is...they go through great risks to make everyone know someone tried to murder the wife too, making it obvious that there is a killer at large, which only makes the investigation more stringent and most importantly, keeps the police on the premises for surveillance preventing them from disposing of the weapon (like almost everything in this episode's plot it is not a flaw of the original story, but of the dramatization, who added practically every minor character).
Continuity mistake: At the end of the 'lovely day' with the Countess, Poirot stops a cab and opens the door for her. Just before the cut, notice a woman with a white dress and a brown hat crossing the street in front of the taxi. The extra crosses the street again in the same direction when he says "Oui" in the following shot. (00:28:50)
Continuity mistake: During the exhibition of the much acclaimed contralto, at one point it is shown that Lady Runcorn is going upstairs and is looking at the smoking person. Back to the host who is on his own at his table. At the first cut, suddenly there are more people standing in attendance in the background (pretty much everyone was seated earlier) and his glass has also refilled. (00:10:15)
Factual error: Poirot is visiting an art exhibition with the Countess, and expresses his admiration for a painting by Marc Chagall. Amazingly enough, that painting is "Les Plumes en Fleurs", something Chagall will create in 1943, years after the time when this pre-WW2 episode takes place. (00:24:50)
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: During the party, the colonel expresses to Poirot his disappointment for the jazz record being played, music "from the inferior races." He puts a tart in his mouth, closing his lips past the piece of fruit. Cut to the wider shot, and he is still holding a tart that sports the strawberry he just chewed on. (00:19:00)
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: Poirot enters Japp's office when the inspector is dealing with the tribulations of modern machinery. As Poirot sits down, you can notice the crumpled paper by the phone being different in the reverse shot, when you can also see Japp's hand being at the corner of the typewriter. But he brings it up from his lap in the next shot. (00:38:15)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: Poirot and Hastings are in front of the corpse at Marsdon Manor. When Miss Rawlinson makes her comment about him taking advice, she is almost with her back against Hastings and in a dramatic light totally different from what shown in establishing shot. (00:17:45)
Factual error: Hastings and Miss Lemon decide to investigate on their own. In the outside view of the first suspect they go question, a large contrail is visible on the left of his building (contrails were not a complete impossibility in the 30s, but it's rather odd to randomly see one in an establishing shot for this timeframe). (00:22:40)
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: In the flashback during Poirot's narration, the scene with Colonel Curtisstalking to the victim at the military club happens differently from the first time around, with Clayton switching hand position after a different line of dialogue, starting off in discontinuity with the previous shot (originally the continuity was flawless). (00:44:40)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: The morning after his arrival at the village, Poirot sits with Hastings for breakfast (prime minister Baldwin is mentioned on the radio). Hastings is holding the newspaper with his left hand and the right is on his knee. New shot and both hands are on the table. It keeps happening during the scene. (00:14:25)
The Tragedy at Marsdon Manor - S3-E6
Revealing mistake: In the reveal at the end of the episode we see a prolonged close-up of the newspaper "Nairobi Daily Press." Not only the fateful article linked to the murder is written in a font different and larger from the one used in the rest of the first page, but you can also see where the fake part abruptly ends, resuming mid-sentence the article of a real (or realistic) newspaper used as base for the prop, back to the right font and consistent style. (00:50:30)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: Poirot holds the widow's painting for Hasting and asks "You do not see?" In the reverse angle with Hastings (obviously) not seeing a thing, Poirot's hand in frame is holding the painting differently. (00:39:15)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: The car with Poirot and Hastings enters the village. Right as the camera begins to pan to the left, notice a woman with a maroon tailleur and a powder blue hat. She walks in the same direction of the car but turns around a moment later. Several seconds after, when we see the two protagonists in the car, the same woman can be seen amongst the passersby through the back window. (00:04:15)
