The "locked-room" or "impossible crime" mystery is a type of crime seen in crime and detective fiction. The crime in question, typically murder ("locked-room murder"), is committed in circumstances under which it appears impossible for the perpetrator to enter the crime scene, commit the crime, and leave undetected. The crime in question typically involves a situation whereby an intruder could not have left; for example, the original literal "locked room": a murder victim found in a windowless room locked from the inside at the time of discovery. Following other conventions of classic detective fiction, the reader is normally presented with the puzzle and all of the clues, and is encouraged to solve the mystery before the solution is revealed in a dramatic climax.
The prima facie impression from a locked room crime is that the perpetrator is a dangerous, supernatural entity capable of defying the laws of nature by walking through walls or vanishing into thin air. The need for a rational explanation for the crime is what drives the protagonist to look beyond these appearances and solve the puzzle.
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