Locked-room

A locked-room is a plot device where a crime (typically a murder) is committed in a place where it is seemingly impossible for the perpetrator to have gained access to it or to have entered or left it without being detected. A locked-room could be a matter of physical isolation where a person is found dead in a room and the only key is in his pocket, or a matter of virtual isolation where witnesses are certain no one except the dead person entered the room. Typically, the prima facie conclusion is that the person in a locked room must have committed suicide. The challenge for the investigator is thus to show how else the person could have died.

Examples of locked-rooms in the stories of Agatha Christie

 * The Market Basing Mystery
 * Murder in the Mews
 * The Dream - witnesses were certain no one else except the dead person had entered the room from the time he was last seen alive.
 * Dead Man's Mirror
 * The Second Gong
 * Murder in Mesopotamia
 * Hercule Poirot's Christmas