This is a great short story, so I wouldn't let my summary that I am about to give stop you from reading it. Like all of Poe's short fiction, it manages to combine successfully fear and a sense of supernatural wonder with a Gothic setting that creates a brooding, terrifying atmosphere. In this story we are plunged into a medieval world that is plagued by an extremely contagious illness known as "The Read Death." In spite of the way that it is sweeping through the land, Prince Prospero believes he can save himself and his courtiers, and for this purpose, locks himself and his followers away in a castle where nobody can enter or leave. Here he lives a life of luxury, throwing one particular party which is described in this story. At this party, there are seven rooms, each with a different colour, the last room being black. This room is so terrifying because of the colour and the big ebony clock that chimes out the hour that few enter. Prospero notices a guest at this masque ball dressed as the Red Death. So outraged is he that he pursues this uninvited guest to the black room, where the guest reveals himself literally as the Red Death. Prospero falls dead, the disease enters the castle and all die.
Poe is using this story not only to terrify but also to show the vanity of the rich and powerful and their illusions of invulnerability. Prospero learns the hard way that wealth and privilege cannot shield him from death. To fully understand the story though you need to consider how the setting works symbolically, especially the way that the seven rooms are described. Hope you enjoy this excellent tale when you read it!