Episode #4.1 - S4-E1
Plot hole: When DCI Roz Huntley kills Forensic Coordinator Tim Ifield the crucial piece of damning evidence is her DNA under his fingernails after scratching her arm. Problem being, at the time of his murder, he was wearing surgical gloves. (00:56:40)
Plot hole: The police are looking for school shooters who wore unicorn masks. There are cell phone recordings of the individuals shooting and I believe CCTV recordings from inside the school. There is a forensic science technique of accurately estimating suspect(s) height(s) using CCTV/camera recordings and math to determine the height. The police could have further narrowed down their pool of suspects by using this forensic method, but they are going at the students blindly chasing dumb leads.
Episode #2.6 - S2-E6
Plot hole: Laura is spotted at an airport where it is assumed she goes to Edinburgh. Although she mentioned later on she broke her bail by leaving the 30-mile radius by her bail conditions. This wouldn't have been possible as part of her bail was to surrender her passport.
The Assassin - S6-E8
Plot hole: There's no way Shelley Hack could clean up all that mess of blood and three dead assassins with only an hour or so before her dinner party.
Plot hole: The bad guy somehow knows what is going to happen (via the sketches) even though the events haven't happened yet, like knowing Mrs Peel was going to show up at Pool's mansion in that catsuit and hat, and that the scenes were going to play out like the sketches.
Second Sight - S4-E7
Plot hole: Kimble enters the bar in the midst of a fight between photographer Howie and a man he tried to blackmail. Kimble comes in too late to hear what the scuffle is about, yet after breaking it up, he somehow knows all about the incriminating photo that sparked it. (00:06:00)
Plot hole: In the pilot, it is established that the surface of anything/anyone made invisible by "quicksilver" is freezing. (Darien gets caught in the women's shower because the mist freezes on him. He freezes the beer mugs for the doctors.) But in later episodes, nobody notices him standing invisible - and freezing!? - next to them.
The Spores - S2-E7
Plot hole: Hal and Roy could not open the spore case with an electric power drill, but later a married couple pops it open with a hammer and chisel, then much later some children acquire the case and easily open it.
Plot hole: Someone as careful and controlling as Timo would never force anyone into working for him, for exactly this reason.
Plot hole: Tom discovers Claire's body in the wardrobe of his motel room. He leaves the room, and within a minute returns to the room, accompanied by the police. The body has vanished from the wardrobe, but given how little time Tom was away from the room, it is impossible for someone to have moved it, particularly given the weight of a corpse.
Woman in the White Hat - S2-E4
Plot hole: Ronnie and her daughter, and son-in-law spot a pick-up truck towing a large trailer through her plantation. Ronnie runs to her truck to investigate. When she arrives, which could only be a few minutes behind the truck and trailer, there are technicians well into the process of mixing chemicals.
Plot hole: After Jack's wife disappears for a couple of days, he receives a call from her cell phone from the cab driver who found it. Jack arranges to pick it up from a hotel. After he picks up the phone, its battery dies as he checks it, at 12:13pm. In the next scene with Jack, he's in a bar with the phone plugged into a charger; when it comes on, he checks it - the battery shows 3%, but the time is 9:13pm. He apparently wasted 9 hours when he's in pursuit of his wife's mysterious disappearance before plugging in the phone. A scene later, the time is now just a minute later at 9:14pm but the battery is now charged to 79%. (00:37:25 - 00:40:45)
Plot hole: After discovering the cards tossed into the ocean at the docks, Miss Dorothy goes to Jaden's dorm to alert him of this. There was no real reason for her to go to him, seeing as how she had no idea if this incident was tied to him specifically. (00:09:05)
Plot hole: Episode 1: All passengers on cruise ships have a passenger card with their name and cabin number imprinted. They are not just identical key cards like in hotels.
The Night of the Raven - S2-E3
Plot hole: Antoinette is making miniature clothes for the soon-to-be shrunken West, but when West drinks the antidote to make him normal-sized, he is wearing the same clothes which would have been shredded as he grew back to normal size.
Episode #5.2 - S5-E2
Plot hole: Collision between the two planes would have been prevented by TCAS (traffic collision avoidance system) computer systems installed on both planes. The TCAS systems automatically coordinate with each other and issue a TA (Traffic Advisory) with an audible "TRAFFIC, TRAFFIC", then if on a course that could result in a collision or near miss, issue an RA (Resolution Advisory) to their respective flight crews. Typically one plane's flight crew is audibly ordered to "DESCEND, DESCEND" by its' TCAS and the other plane will be instructed to "CLIMB, CLIMB" by its' TCAS. The flight crew is required to follow their TCAS instructions over the air traffic controller's. All commercial airliners are required to have a functioning TCAS computer. These systems were obviously not under control of the terrorists, they were conveniently ignored in the plot. (00:03:20 - 00:06:47)
Royal Jelly - S2-E1
Plot hole: It's all very well for Albert to humm "bzz-bzz" to indicate that he has been eating too much Royal Jelly and is no longer entirely human. But "bzz" is just the noise of bees flying, it's not a sound that they deliberately produce. It makes no sense to SAY "bzz." Suppose he was turning into a horse instead, then he might say "Whinny!", but he wouldn't say "Clip clop clip clop."
Is the Total Black, Being Spoken - S2-E3
Plot hole: Jimmy was willing to give Cathy $10k in cash for her troubles and to help her out. She wanted to sell drugs instead of getting his charity. Now he's having a problem fronting her the same amount of money worth of drugs. He's saying his dealer will hurt him if he doesn't pay him back. Makes no sense how he had $10k to give her and now he needs her to pay back the $10k front of product he gave her. What happened to his $10k worth of charity? Why can't he use that to pay it off? (00:42:04 - 00:43:25)