How does the mood of the story change from the Halloween pageant to the walk home?

The night of the pageant, in Chapter 28, is filled with foreshadowing of the violent events to occur. Before the children leave, Aunt Alexandra has a feeling that something is going wrong and Scout notices a strange look pass over her face. Alexandra blames it on "someone walking over her grave". The intense darkness of the night also creates a sense of foreboding, as does Scout's inability to see things around her, trapped inside the large, bulky costume. Then, Scout misses her cue, and ends the night upset and embarrassed. When she and Jem turn around to go back for her shoes, the school lights go out, leaving the children alone in the darkness.

The attack occurs all around Scout and the sense of her helplessness makes the account of the violence more intense. Though the book began with a fear for the monstrous, phantom-like figure of Boo Radley, this chapter solidifies a reversal: Boo becomes the children's savior against the real evil, a human man. One reason that Dill dwells in fantasy rather real life is that nothing can be as frightening in fantasy as it can be in reality. Now that the children have grown older, they come to know vividly that the real source of evil to be concerned about comes from their fellowman, not from imaginary ghosts.