Amanda tries to make Maniac Magee popular in the East End so that the racist bigots that want him gone will no longer antagonize Maniac and the Beales.
Maniac is homeless and colorblind. I don't mean scientifically colorblind. He doesn't see race and different races as anything to get upset about, so when the Beales offer Maniac a place to live, Maniac is super excited. Not only does he have a place to call home, but he loves the Beale family. They love him as well, and they treat Maniac as one of their own. Unfortunately, not everybody in the East End is as besotted with Maniac as the Beales are. Maniac is a white kid living in a black neighborhood, so some East End people start to antagonize the Beale family by putting racist graffiti against white people on the Beale house.
Amanda comes up with a plan to make Maniac popular. He is going to solve Cobble's Knot. If he does that, then the entire town will love Maniac and practically worship him as a local hero. Nobody will want Maniac to leave the East End then.
"So you see," said Amanda, "if you go up there and untie Cobble's Knot -- which I know you can -- you'll get your picture in the paper and you'll be the biggest hero ever around here and nooo-body'll mess with you then."