Basic Trope: An event happens in an isolated area with all reasonable causes of it appearing impossible.
- Straight:
- Alice's corpse is found in her bedroom with a gun wound, but the door to the room is locked from the inside and there's no gun. There's also no window. And also no bullet hole in the wall. Amateur Sleuth Bob needs to discover a counterintuitive way for how the door could have been locked.
- A box with jewels disappears from Alice's bag, which she has left at the entrance. Everyone, including Alice, was at the meeting the entire time and no new person could have entered the building, but when Alice returns the box is gone.
- Exaggerated:
- Alice's room is an unrecognizable mess and has several corpses. Everything was confirmed to be in order just a couple of minutes ago. Every theory Bob checks seems to be anticipated by the culprit and proved impossible. Even Utility Magic has rules that make their use here unlikely.
- By the time of discovery, the door to Alice's room is covered by a wall of bricks.
- In a Ten Little Murder Victims, every victim is found in a different impossibly-locked room, to the point that there's also nobody left to suspect.
- Downplayed: It seems nobody could have entered Alice's room, but a butler reveals right away that a master key has been missing, reducing the questions to only "who" and "when".
- Justified: The culprit goes out of their way to make a seemingly impossible crime scene. Even if only their alibi is lacking, they can't be arrested if Bob fails to explain how have they done it.
- Inverted: A Room Escape Game with seemingly no exit.
- Subverted:
- The door is assumed to be locked and speculation ensures, before the person who has discovered the body clarifies that the door was unlocked, so anyone could have done it.
- Everyone remembers that they are mages and anyone could have locked the door with Utility Magic.
- The culprit confesses how the trick was done right away.
- Double Subverted: When the method of committing the crime behind a locked door is solved, it's revealed everyone with their luggage has checked in by the metal detector beforehand, so next Bob has to figure out where the impossible wound came from.
- Parodied: Bob finds Alice in her room and assumes she's dead. She is clearly sleeping, but Bob goes through several cases of Insane Troll Logic theorizing how the imaginary culprit could have entered the room.
- Zig-Zagged: Bob discovers ways to enter the room without the room's designated key. One by one, they don't work.
- Averted: How the crime was committed is clear at first glance and isn't a problem.
- Enforced: The work is a Mystery Fiction and producers ask to include a locked room as a plot point.
- Lampshaded:
- Bob says that asking the building's staff would be a waste of time because any other normal ways to enter the room are unlikely.
- When Alice's corpse is discovered, Bob hopes she doesn't have the only key.
- Invoked: The culprit is a Theme Serial Killer who likes to challenge people with puzzles.
- Exploited: The culprit is Genre Savvy in Mystery Fiction and knows that if they frame someone from the staff, the police are unlikely to pursue another possibility.
- Defied: Alice has a justified fear that she may be murdered soon and asks Bob to check the door for any secret defects and to ask the staff to verify the safety of master keys. Either Alice survives or Bob deduces the method right away.
- Discussed: At the The Summation, Bob brings up different cases of locked room murders in Mystery Fiction, one of which is exactly what happened here.
- Conversed: "It appears to be an impossible crime, but I assure you that there must be something with the door that allows locking it without the key."
