What is the conflict in Egdar Allan Poe's "the masque of red death"?
I would describe the conflict in "the masque of red death" as control vs. fate.
While Prospero was trying to take control of the situation by isolating himself in a castle with his friends, and took control of his subjects through lavish entertainment, and controlled every color and look in the castle, he could not control what fate had in store for him, no matter how much detail he put into consideration.
The story follows Prince Prospero's attempts to avoid a dangerous plague known as the Red Death within seven rooms of his abbey. Each room is decorated in a different color, the one room into which the guests are reluctant to go is decorated in black and lit with a red bulb. In course of the Ball, a mysterious figure enters and makes his way through each of the rooms. When Prospero confronts this stranger, he falls dead.
The story contains most of the conventions of Gothic Fiction. It is often analyzed as an allegory about the inevitability of death. I would caution a certain amount of care with an allegorical reading because Poe himself disliked didactic literature. Many different interpretations have been presented, as well as attempts to identify the true nature of the disease of the Red Death.– The disease may be a portrayal of consumption.
If the story really does have a moral, Poe showed restraint by not explicitly stating that moral. For those looking for the moral, it is there, while for others it has no message apart from the inevitability of death.