It was then, however, that the Prince Prospero, maddening with rage and the shame of his own momentary cowardice, rushed hurriedly through the six chambers, while none followed him on account of a deadly terror that had seized upon all. (13)
Prospero's rage gives him courage. He is the first and only one of the masqueraders to overcome his fear and take action. Everyone else is in the grips of a "deadly terror." The fear continues to rise.
But the Prince Prospero was happy and dauntless and sagacious. When his dominions were half depopulated, he summoned to his presence a thousand hale and light-hearted friends from among the knights and dames of his court, and with these retired to the deep seclusion of one of his castellated abbeys. (2)
Poe nowhere mentions fear as a potential motive for the retreat of Prospero and his friends. Prospero himself is "happy and dauntless and sagacious," and his courtiers are "hale and light-hearted." Quite a rosy picture. Yet it seems like their deepest reason for fleeing is that they're afraid to die, doesn't it?
and, while the chimes of the clock yet rang, it was observed that the giddiest grew pale, and the more aged and sedate passed their hands over their brows as if in confused reverie or meditation. (5)
The eerie chimes of the big black clock seem to be another reminder of death – they indicate that time is passing. This also makes the revelers nervous…particularly the ones who are closest to death (the "aged and sedate").
But in the western or black chamber the effect of the fire-light that streamed upon the dark hangings through the blood-tinted panes, was ghastly in the extreme, and produced so wild a look upon the countenances of those who entered, that there were few of the company bold enough to set foot within its precincts at all. (4)
The nervousness of the revelers around the black room is worth noting. It seems to suggest a certain skittishness towards anything that reminds them of death.
But to the chamber which lies most westwardly of the seven, there are now none of the maskers who venture; for the night is waning away; (7)
As the night draws on and the midnight hour approaches, the nervousness of the revelers increases. Whereas before there were few willing to go into the black room, now there are none. This helps to create a sense of mounting fear.
But from a certain nameless awe with which the mad assumptions of the mummer had inspired the whole party, there were found none who put forth hand to seize him; so that, unimpeded, he passed within a yard of the Prince's person; and, while the vast assembly, as if with one impulse, shrank from the centres of the rooms to the walls, he made his way uninterruptedly, but with the same solemn and measured step… (13)
The crowd is too afraid of "the mummer" to obey Prince Prospero's order. They all shrink away from it. Prospero himself is no exception.
Then, summoning the wild courage of despair, a throng of the revellers at once threw themselves into the black apartment, and, seizing the mummer, whose tall figure stood erect and motionless within the shadow of the ebony clock, gasped in unutterable horror at finding the grave-cerements and corpse-like mask which they handled with so violent a rudeness, untenanted by any tangible form. (13)
When Prospero falls, at last a group of revelers overcome their fear and attack the guest who's killed their Prince. They discover, to their "unutterable horror," that the creature in the costume is the Red Death itself. The fear level has now reached its climax.
When the eyes of Prince Prospero fell upon this spectral image (which with a slow and solemn movement, as if more fully to sustain its role, stalked to and fro among the waltzers) he was seen to be convulsed, in the first moment with a strong shudder either of terror or distaste. (10)
Prospero's own first reaction is more ambiguous than that of the rest of the revelers. It could be disgust, but it could also be terror. It's certainly clear that he's surprised and unnerved by the Red Death masquerader.
No pestilence had ever been so fatal, or so hideous. Blood was its Avatar and its seal --the redness and the horror of blood. There were sharp pains, and sudden dizziness, and then profuse bleeding at the pores, with dissolution. The scarlet stains upon the body and especially upon the face of the victim, were the pest ban which shut him out from the aid and from the sympathy of his fellow-men. And the whole seizure, progress and termination of the disease, were the incidents of half an hour. (1)
Poe tries to create an atmosphere of fear right at the beginning of the story. This is just about the scariest depiction of death you could imagine in a paragraph – look at his emphatic use of words like "hideous" and "horror." And right away he's also mirroring the fears of the reader in the fears of the people in the story. They're so scared of the Red Death they won't help or sympathize with each other.
And the rumor of this new presence having spread itself whisperingly around, there arose at length from the whole company a buzz, or murmur, expressive of disapprobation and surprise --then, finally, of terror, of horror, and of disgust. (8)
The new masquerader – the guest in the Red Death costume – makes everybody uneasy, especially since he appears at the stroke of midnight (when they're already nervously stopped at the sound of the clock). Notice how their reaction changes from one of mere surprise or disapproval to actual terror. The sense of fear continues to grow.