Two major events are the race with Mars Bar and Amanda’s book being destroyed.
Maniac Magee is very episodic, meaning that the book is really a series of loosely connected events. Two that can be considered important are when Maniac made an impression on the neighborhood by beating Mars Bar in the race, and when Maniac left the Beales because someone destroyed Amanda’s favorite book, the encyclopedia Volume A.
Maniac ran away from home when his parents died and he was left with a feuding aunt and uncle. He just started running one day and didn’t stop. He ended up in Two Mills, a town strictly divided by race. Maniac is white, but he does not seem to notice what color other people are. He is homeless after all. In Two Mills, there is the West End and the East End. If you are white, you should stay on the West End, but Maniac somehow ends up on the East End.
Maniac meets a kid named Mars Bar in the East End. His name comes from his love of candy bars, and he considers himself tough. Maniac baffles him by taking a bite out of his candy bar. One day Maniac ends up racing him, and he doesn’t know what to do so he runs backward. Mars Bar is humiliated that Maniac beats him running backward.
Maybe it was that simple. After all, who asks why otters toboggan down mudbanks! But that didn't make it any less stupid or totten a thing to do. The hatred in Mars Bar's eyes was no longer for a white kid in the East End; it was for Jeffrey Magee, period. (Ch. 38)
Maniac has no meanness in him, and he really did not intend to embarrass Mars Bar. Maniac just doesn’t seem to really understand how to be normal. He may have made an enemy out of Mars Bar, but he thrilled the neighborhood kids.
The second incident actually happens first, but it is more important thematically.
Maniac ends up living with the Beale family for a while. He loves to read, and especially gets along well with Amanda Beale, who loves books so much that she carries her entire library with her so that her siblings won’t ruin the books. She lends Maniac a book and Mars Bar tears a page out of it, so she beats him up.
Maniac loves the Beales. They understand that he desperately needs a place to belong. Unfortunately, there are some that just do not understand the concept of a white boy living with a black family. The Beales are targeted, and the last straw for Maniac is when Amanda’s favorite book, Volume A of the Encyclopedia, gets destroyed as a message to him.
More than anything, Maniac wanted to hug Amanda and tell her it was okay. He wanted to go inside, be with his family, in his house, his room, behind his window. But that wasn't the right thing. The right thing was to make sure the Beales didn't get hurt anymore. He couldn't keep letting them pay such a price for him. (Ch. 21)
Maniac leaves because he doesn’t want the Beales to be the targets of racism or violence. It breaks his heart, but he cares more about them than anything. He ends up fluttering around, even living at the zoo with the groundskeeper until the old man dies. Finally, Maniac returns to his real family, the Beales.