The plot of 'The Masque of the Red Death' is actually quite simple. The Red Death is a fictional plague sweeping through the land. Prince Prospero, the main character in the short story, is hiding from the plague in an abbey, along with a bunch of other nobles. Despite the plague being quite horrific and consisting of symptoms like sweating blood and dying within 30 minutes, the nobles think they are safe in the abbey. In fact, they are so relaxed about their situation that Prospero hosts a big masquerade ball.
The only downside of the abbey, which is quite luxurious, is the decor. There are seven rooms which are color-coded and arranged east to west. The last of these rooms is a creepy room that is decorated in black and scarlet. This room contains a huge clock that scares the guests whenever it chimes on the hour.
The clock does not disrupt the masquerade for long, however. People keep partying until it strikes midnight. Then, a mysterious figure shows up, which is disturbing because the doors to the abbey are welded shut to keep all the plague-infested people out. The figure is dressed in a bloody robe, and the figure's mask is designed to look like someone who has died from the Red Death.
Prospero chases the figure through the abbey until he corners the figure in the creepy room, which is the room farthest to the west. When the stranger looks at Prospero, Prospero drops dead. The other noblemen corner the stranger and unmask him. Once he is unmasked, they realize that he does not possess a body. Everyone in the abbey catches the Red Death and dies.