Prince Prospero has done everything in his power to bar death from his castle, so when he sees a man seemingly dressed up in imitation of a corpse that has died from the Red Death, he is shocked and horrified at the sight:

his broad brow, with all the features of the face, was besprinkled with the scarlet horror [of the Red Death].

The prince first shudders with fear and disgust, then becomes very angry. He wants his many guests to rally and unmask the intruder, but the terrified guests let the man walk unstopped between them. This leaves the prince to deal with the problem on his own. He moves from fright and rage to rage alone. We learn that

Prince Prospero, maddening with rage and the shame of his own momentary cowardice, rushed hurriedly through the six chambers . . .

The prince chases the seemingly masked intruder with his upraised dagger to the final, black velvet chamber. But instead of killing the intruder, the prince himself drops dead. The intruder is Death itself, come to get the partiers, all of whom follow the prince into the black room and die. The prince's rage at the presence of Death cannot stop it any more than could the high walls and barred doors of his castle.

Prince Prospero is outraged by the appearance of the midnight guest in the story. He is hosting a ball full of characters in splendid costumes, but the garb of the midnight guest is too much for him. The man is wearing a dark black cloak, with blood daubed around the mask and face—which is appalling and not at all appropriate for a high society ball.

So, Prince Prospero decides to apprehend the guest after his arrival. He demands that some of the guests pursue and capture him, but they refuse. So Prospero ends up grabbing a knife and pursuing the masked figure himself. He chases him throughout the building and attempts to capture him. When he finally comes upon him, though, he realizes there is no man beneath the cloak, and that the figure was Death itself. Learning this, Prospero drops down dead on the spot.

The "midnight guest" is costumed in a black shroud-like garment, hiding all but a masked face which is made up with daubs of blood to look like someone suffering from the Red Death. The other guests are frightened by the appearance of this newcomer. Prince Prospero is appalled by the guest's appearance, and his horror gives way to outrage as he determines to punish the masked intruder for his insolence and effrontery. He first asks other guests to seize the intruder, but they are intimidated and frightened and refuse to do so.

The Prince decides to take matters into his own hands and, wielding a knife, begins to pursue the strange guest. Just as occurred earlier with the courtiers in attendance at the ball, the Prince goes through each differently-colored chamber in pursuit of the midnight guest, only to find, once they reach the last black-walled room with blood-red windowpanes, that there is no form beneath the shrouds of fabric. The intruder who had been costumed as Death personified is not a human being at all. But it would appear he/she is also not merely an illusion, because Prince Prospero suddenly falls down dead, showing the ravages of the Red Death on his face. The ebony clock strikes midnight, and each reveler begins to writhe in anguish as the Red Death consumes them all.

Initially he is frightened; however, he overcomes that and is outraged.  He storms after the masked figure, ordering his revelers to seize him, though they refuse.  Overcome with anger at such an insult, Prospero draws his dagger to stab the figure.  However, when he grabs the figure and spins him around, he sees that it is really the Red Death itself and Prospero drops dead.