The Mysterious Affair at Styles - S3-E1
Plot hole: Can't fault this massive plot hole to the adaptation, but to the source material; the culprit (forgetting the stupidity of writing an incriminating letter detailing the plan to murder someone, and put it in a desk he shares with her) since there are people outside the room that are about to enter, tears the letter in 3 neat vertical strips, rolls them, puts them in the vase on the mantlepiece, and then opens the side door to slip away...instead of simply pocketing the letter and going through that same door. Nobody was going to search him or anything and could have burned it, torn it into confetti, anything, later. It takes way way longer to do what he did, which needed him to stay there in the room increasing the chances of being found out. And of course he and his accomplice do not retrieve the letter after.
Plot hole: The hole in the hat was pre-existing and the bullet was fired in advance and dropped. Poirot notices immediately the hole when Nick puts the hat down but somehow missed it while she was wearing it as she supported him. He also does not notice that the bullet has not been fired at that time - which would have been still hot if just fired, not at all if dropped. Most importantly, in the spot where they were sitting, it's not even possible to think where a shooter could have ever been hidden; nobody wonders where the mysterious shooter could have been or cares to investigate the circumstance despite knowing the very moment the supposed shot happened. The fact is basically ignored throughout the rest of the episode.
Plot hole: Nobody hears the sound of a gun being fired past a door they were waiting almost in front of, and the police cannot tell apart a shot fired point blank by one fired 20 feet away and probably at a very sharp angle. Moreover, the bleeding should be all over his face, since leaning the way it is shown in this adaptation is most likely to lead the victim to fall over, and even leave bloodstains out of the window and on the ground below, which someone would have noticed in the crowded factory.
The Million Dollar Bond Robbery - S3-E3
Revealing mistake: All the Liberty Bonds loaded in the bag of Mr. Ridgeway have the exact same serial number. (00:20:00)
The Adventure of the Egyptian Tomb - S5-E1
Factual error: In the scene after Poirot pretends to be poisoned, a person folds the modern flag of the Arab Republic of Egypt instead the flag of the Kingdom of Egypt as it was at that time.
Factual error: Attention to detail in props is always extremely high in this series, and tubular flashlights have been in circulation since the beginning of the century. However the one that the supposed burglar is holding as they make their way through the top floor of the villa looks perfectly modern and unlike any model compatible with the 30s. (00:10:20)
Continuity mistake: Poirot is holding up a letter in an envelope. He turns it to show the front to Lady Mayfield. The flap of the envelope appears to be tucked in. The shot cuts to a close-up, but now the back of the envelope is facing Lady Mayfield and the flap is sealed. He then turns the envelope to show her the front. (00:44:20)
Hercule Poirot's Christmas - S6-E1
Character mistake: After Japp's arrival, when Poirot walks up the stairs with the two male detectives, at one point he says "Mais no madame." ("But no mylady.")
Revealing mistake: As the major tries to convince the Chief Inspector to leave the island, we see Hastings come down the stairs. However, prior to this we can see Hastings waiting just out of shot for his cue to enter. The edge of his hat is visible for several seconds, and when he's cued he begins walking into the shot. (01:15:27)
Plot hole: Since the Countess was the only person to be at every dinner when the jewelry thief was in action, it takes a very special kind of idiot to not identify her as the culprit. Japp here did not need at all Poirot's acumen, but simple due diligence cross-checking the guest lists, something there is absolutely no reason he wouldn't do, and yet she is never treated as a special suspect. Also, Japp's job is described as being in jeopardy after the first 3 thefts, a 4th happens, he does not quite solve it (but retrieves at least the necklace), but he's off the hook despite the thief being unidentified, at large and with still the jewelry stolen from the first 3.
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: When Poirot pulls out of the drill hidden in the handle, he holds it triumphantly in his right hand. In the next shot he mounts it on the handle starting the motion with the drill already in the left hand and the rest of the gimlet in the right. (00:40:00)
The Underdog - S5-E2
Factual error: Lily looks over part of the procedure for the manufacture of Astroprene. There are several problems with the chemical structures shown in step two of the procedure. This step appears to be a simple acid catalyzed rearrangement of the molecule shown. The procedure should begin with a C inside the hexagonal ring and end with the C outside the ring with no other changes. The errors include, among other things, a carbon atom at the lower left of the ring with two lines (bonds) to it. The C should have four bonds (lines), the two shown plus two to hydrogen atoms (H). The bonds to H may be condensed so the C will look something like -CH2 - (the 2 would be a subscript). (00:10:30)
The Adventure of the Cheap Flat - S2-E7
Plot hole: The professional hitman from the US does not have a gun of his own, and does not bother in the long time elapsed between the apartment's hit and the nightclub (it could even be hours) to check if the gun he just grabbed is loaded or not. Who in the world would not take a split second of his time to peek at the cylinder and see how many bullets does he have? An assassin planning to kill with that gun, even.
Audio problem: There's a bit of a mix-up in the codenames of the cars who chase Reggie Dyer. Unit 7 is the first to give chase and it is identified by its crew with the photographer. Then Unit 8 intercepts at the rendez-vous point. Check the license plate; FVW 49. Japp mentions a "unit 10" that is not shown. Later in Chinatown, Japp calls for the other cars, and "Car 8" responds, but its license plate is now YD 8501 and it's another car model. Unit 10 is again not shown. They dubbed in the wrong voiceover, they should have kept offscreen the second response by Unit 8 and made it Unit 10's.
Factual error: In Poirot's study, Lord Pearson shows the big piece of mineral, saying "You're left holding a a nugget of top-grade 24-carat silver." That's a laughable blunder, from a top level banker and investor about to do a massive mining deal even. Silver purity is expressed in millesimal fineness. (00:11:30)
Factual error: The episode is set at a precise date (it's even a plot point); 8/2/1935. But at the beginning Poirot and Hastings are playing Monopoly, and right there on the board you can distinctly read; "Trade Mark - Pat.app. For Nº 3796-36." As signaled by the last 2 digits, it's a 1936 edition (the UK localization of the game). (00:01:40)
Character mistake: In the hotel lobby, Poirot, indignant of Hastings' attitude towards the murder case, says "After three attempts had been made at the life of M. Nick, Poirot gave his word he would protect her." But he did that after four attempts; Nick already avoided 3 "mysterious accidents" (painting, car, boulder) and Poirot witnessed the 4th, the bullet that pulled him into the whole case to begin with. (01:02:20)
Continuity mistake: As Poirot stands from the late dinner with the young socialites to go talk to Inspector Japp next to the door, he leaves his napkin on the table. The napkin changes between shots, going from mostly straight to crumpled (when Mildred says "How dreadful!") to straight again. (00:22:20)
Four and Twenty Blackbirds - S1-E4
Continuity mistake: When the milkman places the third bottle on Mr. Gascoigne's steps, they are placed in the sun. When the neighbour approaches, the whole road shows no particular sunlight. Which is fine, as a sudden change of that kind is ordinary. When the other neighbour pops by the corner and inquires, there's a close-up of the bottles, and again there's visible and directional light, pointed differently than the first instance. (00:08:45)
The Adventure of Johnnie Waverly - S1-E3
Continuity mistake: When Hastings stops his car in front of the train station at the end of the episode, he talks to Poirot holding his hand on the outer circle of the steering wheel, or on the inner part in the reaction shots. (00:49:20)
