In the beginning of the story we find out there is a pestilence that's called the Red Death and is killing everyone in the dominion. The Red Death causes people to bleed profusely through their pores and die in a half hour.
Prince Prospero invited all of his friends to a masquerade which represents a safe place to take their mind off of whats happening outside.
An intruder shows up at this party and Prospero is angry that he is here.
In this scene Prince Prospero is killed by the Red Death in the last room which is the black and red room which represents death
As the guests try and subdue the intruder they find that there is no one under the mask but a bloody face.
The clock represents the amount of time you have left in your life. The intruder represents the Red Death, and the black and red room represents the last stage of your life.