By this point, Maniac is sure that his presence curses the lives of others. Determined to spend the rest of his life alone and to make that time short, Maniac finds himself huddled in a hut outside an old war monument several miles outside of town. Cold and hungry, Maniac lays there for more than a day, welcoming the end that is sure to come. But on the second night, fate once again takes a turn for Maniac when two young children make their way to the monument where Maniac is staying.
Maniac discovers that the two young boys have run away from Two Mills and are attempting to make their way to Mexico. Maniac becomes worried for their safety and decides he needs to help get them back to Two Mills even though he himself vowed never to return. With bribes of pizza and a secret shortcut to Mexico, Maniac manages to coax the boys back to Two Mills with him only to discover that the two young boys, Piper and Russell, are the younger siblings of John McNabb.
It doesn’t take long for the boys to realize that they are in the presence of Maniac Magee, the boy who humiliated their older brother on the baseball field. To ease tensions and smooth things over with John, Maniac tells the boys that the next day, John pitched a new pitch to him and Maniac never hit it once. This small lie helps bridge a tenuous bond between John and Maniac and ultimately results in Maniac being invited back home with the McNabs.
Maniac soon realizes that the three boys may have it worse off than he does. The boys are motherless and are being raised by an alcoholic father who bothers very little with them. The house is barely livable, with trash and pet waste littering the floors, rotting food crawling with bugs occupying the kitchen, and a giant hole in the floor of the second story just above the living room. The boys, left to their own devices, drink, smoke, and play football throughout the house where furniture is minimal and windows have been boarded over.
Despite being a less than ideal living situation, Maniac ends up staying with the McNabs, realizing that by staying in a place he would never want to belong, he will not run the risk of losing people he loves. During his stay with the McNab boys, Maniac takes on the responsibility of coaxing the young boys to school each week. In exchange for one full week of school attendance, Maniac performs a feat designed by the brothers. Such feats included knocking on Finsterwald’s door and kissing the buffalo at the zoo. As Maniac performs each feat, the boys’ popularity grows as well. By spring the boys have grown more and more creative with their ideas until one day they dare Maniac to do the most incredible feat of all, to go into the East End of Two Mills.
During his time with the McNabb family, Maniac has learned that they have an unreasonable fear of the members of the East End. Thinking that one day the East Enders are going to invade the West End and start a war, the McNabb family has spent all of their time and resources building a brick shelter to fortify their home. Maniac, however, knows better, having spent time with the inhabitants of the East End and having realized that ignorance is the only thing keeping these two parts of town divided. Maniac easily saunters across Hector Street and beyond the invisible divide, causing Piper and Russell to go into hysterics out of fear.
However, Maniac keeps going deep into the East Side, until he runs into Mars Bar. Mars Bar, like John McNab, feels as though he is the toughest person in his part of town and having been shown up by Maniac, he has taken a disliking to him. Mars Bar challenges Maniac to a race, convinced that during Maniac’s absence, he has developed enough skill to finally beat Maniac. However, Maniac not only beats Mars Bar, but also humiliates him further by finishing the race backwards and crossing the finish line while looking at Mars Bar. Not sure why he did it, and realizing a bit too late the fuel he has now added to Mars Bar’s fire, Maniac quickly goes to leave town only to be discovered by Amanda’s younger siblings, Hester and Lester. Hester and Lester convince Maniac to come home with them and spend the night at their house, but Maniac leaves early in the morning, fearing that he would never be able to leave otherwise.
When he makes his way back to the West End, Piper and Russell are genuinely shocked to see him alive and unharmed. Maniac returns to their home and for a time is able to continue to coax them into behaving. But when Maniac attempts to stop their game of “blacks and whites” and convince them that what they believe is not the truth, the boys grow angry and command him to leave their home. Once again, Maniac roams Two Mills alone and homeless. Several days later, however, the boys find Maniac and ask him to Piper’s birthday party, as if nothing had happened. Maniac agrees to go but only on the condition that he is allowed to bring a guest. The boys quickly agree, unaware of Maniac’s intentions.
Maniac sets out to find Mars Bar and convinces him that the only way he can ever prove to be just as "bad" as Maniac is by crossing Hector Street, something only Maniac has done. Mars Bar agrees and follows Maniac into the West End. First, Maniac takes Mars Bar to the home of the Pickwells, a giving and generous family with numerous children who happily invite down-and-out individuals into their home for meals. Maniac had visited the Pickwells from time-to-time and hoped to show Mars Bar the generous and loving side of the West End, before taking him to the McNab home. Mars Bar is treated like a welcomed guest in the Pickwell home. The children clamor to hear stories of all his feats because Mars Bar is almost as great a legend as Maniac to the young children of Two Mills. Mrs. Pickwell receives Mars Bar with open arms.
Unfortunately, the same is not true at the McNab home where Mars Bar is treated with disregard; Mr. McNabb even refuses to stay in the room while he is there. Once Mars Bar learns of the shelter being built and the game the young McNab boys play (“blacks and whites”) he becomes enraged with Maniac and questions Maniac's intentions. Maniac himself is unsure what he was hoping for except maybe some understanding across the divide. Once again, Maniac finds himself without a home or a place to belong. He spends his days at the local library reading, his nights sleeping in the park, the zoo, and even in backyards, and the early morning running through town. Eventually Maniac finds that Mars Bar has been shadowing his runs and it isn’t long before they are running together though not acknowledging it.
One morning, as the two boys are running simultaneously, they are approached by a hysterical Piper. Russell and Piper had been playing a game on the trolley bridge across the Schuylkill River. It was Russell’s drop to shoot rocks from the bridge at a raft carrying Piper on the river. But once the game ended, Russell became paralyzed with fear, unable to climb back down off the bridge and realizing what a dangerous and precarious position he was in. Piper had no doubt that the legendary Maniac Magee, the boy who had knocked on Finsterwald’s door and had easily crossed Hector Street, could rescue his brother. But Maniac, standing for the first time at the spot where his mother and father had died, a place he avoided in all of his travels, simply turned and walked away, unable to face the bridge.
In the end, Mars Bar saves Russell. Mars Bar’s act of bravery causes the boys to regard him in a whole new light and is the beginning of a new Two Mills without an invisible divide. A few days later, Mars Bar manages to track Maniac down at the zoo, where he is once again residing, and brings with him Amanda Beale. Together they convince Maniac that he should live permanently with Amanda’s family and that he has never been a curse but a blessing to the whole town of Two Mills.
Part III is an incredibly important section of Maniac Magee, chronicling Maniac's descent into hopelessness, his necessity in the lives of the McNabs, and eventual acceptance and importance in the history of East End and all of Two Mills.
The reader might regard it as a sign that when Jeffery tries to let himself die, he rouses himself to help others. This scene underscores Jeffery's devotion to others, and, taking into account who he finds, the author shows that Jeffery gives this devotion without regard to age or wealth.
Like Grayson, the McNabs are a family of poor whites, a drunk father and children who are not well educated. This can be seen from the racist remarks made by the family as if they do not recognize that what they are saying is wrong; it is especially clear in the "Rebels" (164) game they play in which kids are assigned as black or white and then fight against one another. And, though Maniac tries to introduce them to Mars Bar at the party, the difficulty he faces shows just how ingrained racism was in people at the time.
Part III, in contrast to the stability Maniac experienced in Part II, is characterized by a total lack of home and of direction. This can be seen literally through Maniac sleeping alternately with the McNabs, at the zoo, and on the porches of strangers. It is also importantly reflected through Jeffery's return to aimless long-distance running. However, Mars Bar beginning to join Jeffery on these runs is a signal that some stability will return to Jeffery's life through Mars Bar's actions and the acceptance of the people of East End.
The climax of Maniac Magee comes in Chapter 44. Piper McNab runs to Maniac and Mars Bar who are on their morning run to say that Russell and he were playing on the train tracks and Russell has now gotten too scared to come down. When this event makes Jeffery remember his parents' deaths, Mars Bar must step up, cross the lines of color separating these families, and save Russell. This event brings the rising moments of Jeffery meeting various people and grappling with his parents' deaths throughout the story, and leads to the resolution of him getting a family and having begun the fusion of Two Mills into a single, truly desegregated city.