In this short story, the main characters might include a young woman who has just moved into an old mansion with a locked door. She is brave and inquisitive. There could also be an elderly neighbor who warns her about the locked door but doesn't explain why. And perhaps there is a mysterious figure that seems to be associated with the locked door, like someone who has been seen lurking around it at night.
There could be a detective - like character in 'the locked door short story'. If the locked door is part of a mystery, perhaps a detective is called in to solve the case. There might also be an old caretaker of the building where the locked door is located. The caretaker might have some knowledge about the door but is reluctant to share it at first.