Prospero believes that he and the nobles of the kingdom can escape death of a very dangerous plague called Red Death. So he invites all of them to his castle for a masquerade ball.
Prospero has different rooms that everyone goes into throughout the night. Then as the clock strikes midnight, a mysterious guest that was not invited appears masked as a very scary and horrific person.
When Prospero confronts the masked figure, he immediately falls to his death. Then the others realize that there is no one under the costume and they all die inside a black room with red windows on the west side. The Red Death has entered Prospero's castle and kills everyone inside.