The mood outside the castellated abbey is dire, hostile, and terrifying as the countryside suffers from the deadly pestilence, which is a frightening disease that causes its victims to bleed from their face and experience painful seizures before dying in a half an hour. The Red Death is said to have decimated Prince Prospero's dominions and the nature of the plague has contributed to the grotesque, horrifying atmosphere. Outside of the abbey's walls, Prince Prospero's subjects are experiencing a hell on earth scenario, which emphasizes the atmosphere of gloom, despair, and fear.
The atmosphere inside the abbey's thick walls is much different from the desperate, horrifying mood of the surrounding countryside. Inside the castellated abbey, Prince Prospero has manufactured a pleasant, carefree atmosphere by inviting buffoons, ballet-dancers, musicians, and one thousand of his closest friends to engage in revelries. Prince Prospero has his abbey securely locked from both the outside and inside, and there are more than enough provisions to last for an extensive amount of time while the Red Death wreaks havoc outside. Poe also comments that inside the abbey, Prospero has a created an atmosphere of "Beauty" and encourages his guests to drink wine and enjoy themselves. Prince Prospero also hosts a magnificent ball, which is a product of his semi-barbaric, bizarre imagination.
The Red Death is a deadly disease for which there is no cure. It cannot be avoided and eventually it will kill everyone because there is no cure. The citizens outside of Prince Proospero's castle are full of grief and echo the sounds of hopelessness, despair and futility. They are mourning the loss of men, women and children and their cries are echoed throughout the streets filled with pain and anguish.
Inside the abbey, Prince Prospero has chosen to celebrate their freedom from the disease by throwing a massive masquerade party for 1000 of his followers. Prince Prospero feels that they are safe from the plague and by fortifying the castle they will prevent their own demise. The Prince thinks that he can beat the hands of time, but the clock strikes and echoes the closeness of their impending death and reminds them that death is an inevitable conclusion to the party. Maybe Death had his own feeling of revenge for those that ignore the cries of their own people.
The mood outside the abbey is one of unrelieved darkness. There is fear of the plague, sadness over those who have died, and despair over all the suffering.
Inside the abbey, " But the Prince Prospero was happy and dauntless and sagacious," and so he invites his healthy and "light-hearted friends" to be with him. They are, at the start of the story, happy and somewhat superior; they are healthy when those outside are dying.
However, later in the story, the prince becomes anxious due the masked intruder (the red death), and eventually he is as scared as those outside, until despair fills his party too.