The narrator establishes that Maniac Magee is a legend -- half true, half myth. Jeffrey's parents die, he endures life with Aunt Dot and Uncle Dan, and at age eleven he runs away at a school musical. After a year of wandering, he arrives in Two Mills.

Jeffrey arrives in the East End, meets Amanda Beale and her family, earns the name 'Maniac' through a series of extraordinary feats -- untying Cobble's Knot, catching John McNab's pitches, returning a lost frog -- and finds himself sleeping in the Beales' buffalo pen at the zoo.

Jeffrey moves in with the Beale family on Sycamore Street in the East End. He experiences genuine family life for the first time -- dinners, baths, a bedroom, a little brother in Hector. But he also confronts the hostility of the neighborhood toward a white boy who has crossed the line, and Mars Bar Thompson's ongoing challenge to his presence.

After leaving the Beales, Jeffrey wanders back to the East End and then to the West End, testing whether he belongs anywhere. He sleeps in the woods at Finsterwald's backyard, risks the legendary Finsterwald terror, and discovers the baseball equipment room at the park, where he finds Grayson.

Jeffrey and Grayson spend the fall living together in the equipment room. Jeffrey teaches Grayson to read; Grayson tells stories of his minor-league career. They celebrate Thanksgiving and Christmas together. On Christmas Eve, Grayson dies peacefully in his sleep, and Jeffrey is alone again.

Jeffrey spends the bitter winter back at the park, barely surviving. In spring, he attaches himself to the McNab family in the West End -- Piper and Russell McNab, wild delinquent brothers, and their father John McNab, the high schooler Jeffrey struck out in Part One. Jeffrey tries to provide the boys with structure, birthday parties, and the literacy he values, but the McNab household is chaotic and nihilistic.

Piper and Russell lead Jeffrey to a trestle bridge over the Schuylkill River, daring each other to walk across the track over rushing water. Piper falls and cannot get off the trestle. Mars Bar Thompson -- who has followed -- is the one who talks Piper back to safety. Jeffrey watches Mars Bar be the hero and something in him begins to shift.

Jeffrey returns to the empty band shell in the park, running again, back to nothing. Amanda Beale hunts him down in the dark, furious and relieved, and demands he come home. Jeffrey, who has spent the entire novel looking for a place to stop, finally stops. The last line: 'He was already there.'