Plot hole: Columbo is in the Pauley's hotel room trying to figure out how the bottle landed upright next to his body after he was shot. Devlin - the murderer - turns up unannounced and uninvited. How did Devlin explain that he knew where the victim was staying when he was murdered? Media reports might have mentioned the name of the hotel but there is no way they would have included the room number.
Under & Out - S3-E11
Plot hole: Gretchen, Lincoln, and Sophia were able to visit Scofield and Whistler in Sona without Gretchen being recognized. She was taken in for questioning in episode 9, but she managed to escape and kill General Zavala and one other guard. The other guards knew that she was the one who killed Zavala but she was still able to sign in for visitation.
Plot hole: In this episode, the Duboises make such a big deal about Ariel being old enough to finally learn to drive. However, two episodes previously ("Things to Do in Phoenix When You're Dead") Ariel drove to school with Joe, and Joe complimented her on her prowess.
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: Hippolyta tells Hawkgirl of Aresia's background of being born in the outside world, the war in her country and right up to her drifting to the shores of Themyscira. It would be impossible for her to know anything of Aresia's background as in part two, it's explained that the captain of the ship who saved Aresia died shortly after reaching Themyscira and therefore would not have been able to tell Hippolyta anything.
Plot hole: A central plot device in this episode is that there is no six letter word made up of the letters EXVIN, so the murdered man cheats at the word game by playing a word he knew to be inadmissible - exvin, a wine connoisseur who no longer drinks. Since he is supposed to be a stone cold killer player at this word game, don't you think he would have thought of Vixen? Sara Sidle points that word out later - why wouldn't a world champion word game player have figured it out, using a safe, common word and avoiding a possible challenge?
Suggested correction: If you watch the episode (timecode 00:36:20), in the flashback it shows exactly why he did not use vixen. There were 2 spaces between the "x" and the "n" on the board, so Adam played a bluff and used the fake word exvin.
Plot hole: If the Lady of the Lake walks every night to her room and kills those in her path, why didn't Flora and Miles' parents die in their room by the hands of the Lady in the Lake when they first moved in?
Plot hole: At the end of this episode Red takes off his shirt revealing his burned back, which leaves us to think that he might be Elizabeth's dad. However, this particular mark should have been noticed and written down in Red's prisoner file when he was taken into custody the first time (Episode 1). In that case Elizabeth would already know that Red is burned and could have asked some questions about it.
And Those We Left Behind - S4-E6
Plot hole: The very ending scene where Peter (in this version died in the ice as a boy so Walter's wife never met him) takes off some of the dust covers then picks up a toy airplane. The toy airplane he got as a child from ... Walter's wife when she was trying to placate him in an earlier episode for trying to run "home". This toy airplane wouldn't have been his as a child in this version of the universe. (00:42:00)
Guy Walks Into a Psychiatrist's Office - S2-E1
Plot hole: In this episode Tony tells Janice that he has just put their mother's house on the market. In season one, the house had already been sold.
Suggested correction: Tony and others say many things that aren't accurate. While season one gives the firm impression that the house is sold, it's not confirmed on screen. There may have been a deal where the intended buyer couldn't get financing or a closing never took place for other reasons.
Strawberries and Cream: Part 1 - S3-E23
Plot hole: In the heat of killing fake Red John, Jane forgot to notice that Craig O'Laughlin never knew about the mall setup to lure Red John. So definitely Gale Bertram himself was in contact with the serial killer which he may have missed first up, but all that time in jail afterwards he could have figured it out.
Plot hole: When Sam and Dean realise they need to destroy the hook to stop the Hook Man, they find out that it has been reforged into something else. They state it needs to be set on fire to stop him, but if it was melted down and reforged then it has already been set on fire and the Hook Man shouldn't be latched on to it in the first place.
Day 2: 7:00 A.M.-8:00 A.M. - S2-E24
Plot hole: Peter Kingsley is shot and killed by a man in a helicopter just as he is about to kill Jack. Kingsley would definitely have heard the helicopter approaching.
Plot hole: Throughout the series, auxiliary characters are always far too willing to give all kinds of information to Tru. Doctors and registrars constantly give her privileged information about patients and students. Tru is often able to retrieve information like addresses and phone numbers from people's service and utility companies, when normally you must verify your own information before they will even talk to you about your account. Of course there can't be an episode if Tru doesn't quickly find the person who asked for her help, even though she doesn't usually know much more than their name, but it's still a bit conspicuous.
Shift Into Turbo: Part I - S1-E1
Plot hole: Divatox and co. live in a submarine in Angel Grove lake. In "Hogday Afternoon", Angel Grove lake was drained to about 30ft at the deepest. The lake would have to be several hundred feet deep for a large submarine to hide there.
Plot hole: The FBI is looking for a "very tall" guy who has been identified as such by various witnesses and by their own expert due to the entry angle of a fatal bullet wound - 6'5" at least. They send Elena into a bar near the end of the show to meet the Albanian perp who when he arrives is barely average height.
Plot hole: Parker gains access to the external room using a valid security card, they figure out the CEO's passcode which opens the burn room door...and yet the room inside is still protected by a swarm of lasers. Was the CEO supposed to dance through the laser sensors like Parker does every time he goes in?