The protagonist of the story is Charles, a young lad who is sick with a cold. Just as the land is beginning to burn from the autumn season, Charles begins to burn from a high fever. Not long after the burning fever begins, Charles feels a nameless terror overtake him. First his hand begins to change. Soon Charles declares that his hand no longer belongs to him, and he begs the doctor to "change it back." But the doctor's procedures are useless, and before long, this terror possesses Charles' entire body. His limbs grow warm, then so hot that the room is filled with the warmth of this feverish change. His lungs catch fire "like burning bellows of pink alcohol," and his room lights up "as with the flickering of a hearth." Charles' lips burn and his eyelids, like leaves, catch fire. Even his nostrils exhale blue flame.
The fire of this fever completely purges Charles of his good qualities. Now he has the evil power to burn other living creatures to death. He begins with a group of fire ants scurrying across the pavement. He touches them with his foot and knows that they lie cold and lifeless. Next, he shakes hands with the doctor and his mother and father. Finally, he pets his yellow canary once, shuts the cage door, stands back, and waits.
Bradbury's use of fire imagery usually depicts the theme of good triumphing over evil. "Fever Dream," however, is presented as an ironic reversal of this theme. Bradbury does depict a regeneration taking place in the young boy, yet this regenerative process changes good into evil. Perhaps this story best characterizes Bradbury's belief in the tremendous force that evil can and will exert on the world if humanity does not eradicate it.