""The Door That Has No Key"" is a mystery novel written by Cosmo Hamilton and first published in 1913. The story follows the wealthy and eccentric Mr. Stephen Lone, who invites a group of people to his country estate for a weekend party. However, things take a sinister turn when one of the guests is found dead, and the door to the room where the murder occurred is locked from the inside with no key.As the investigation unfolds, everyone becomes a...