When Piper invited Maniac to his birthday party, he agrees on one condition. He has a “zany” idea. He tells them he will come if he can bring someone. The someone he has in mind is Mars Bar. The McNabs would never expect him to bring a black boy to the party, and they tell him to bring whoever he wants.
Maniac has a plan. He doesn’t understand the racial divide in Two Mills. He wants people of both races to see that there is no difference between people.
Whites never go inside blacks' homes. Much less inside their thoughts and feelings. And blacks are just as ignorant of whites. What white kid could hate blacks after spending five minutes in the Beales' house? And what black kid could hate whites after answering Mrs. Pickwell's dinner whistle? (Ch. 41)
Maniac first brings Mars Bar to the Pickwell house so he can see “the best the West End had to offer.” Mars Bar is a big hit there. He is polite, and the Pickwell kids love having him.
The little Pickwells made as much fuss over Mars Bar as over Maniac. They believed, as did all little kids in the West End, that he carried a hundred Mars Bars with him at all times. Not surprisingly, Mrs. Pickwell never batted an eye when she saw who was coming to dinner. (Ch. 41)
On the way to the McNab house, Mars Bar demonstrates his feat of stopping traffic. It is also a big hit. Things are going well until they get to the McNab house.
The McNabs and Cobras are unrepentant racists. George McNab demands to know what Mars Bar is doing at the party. Piper breaks the tension when he asks for his birthday present, but the Cobras do not talk to Mars Bar and George says to tell him when "it" leaves.
Despite George’s rudeness to Mars Bar, Mars Bar tolerates them until a fight breaks out when Mars Bar insults the McNab house's smell. Maniac prevents them from fighting. They leave, and Mars Bar demands to know why Maniac subjected him to the McNabs.
"You suckered me. You soften me up with them Pick-peoples, then bring me here. Wha'd you think! I was gonna cry Okay, I come over. I did it. It's done. And don't YOU be comin' 'round no more, ya hear me, fish! 'Cause you ain't only seen me half bad yet." (Ch. 41)
Maniac realizes that he should not have expected a miracle. It would have been better to just bring Mars Bar to the Pickwells and leave it at that. You can’t change deep-seated beliefs overnight. So while Maniac might not have changed the McNabs, he did show the Pickwells that everyone is the same, and gave Mars Bar something to think about too.