Bud is placed in the care of the Amos family who locks him in their shed; he escapes to fend for himself on the streets of Flint, Michigan.
Bud meets up with an orphanage friend, Bugs. They plan to ride the rails together, but Bud falls behind and doesn't make it onto the train. Bugs throws back Bud's beloved suitcase.
Bud decides to walk the 120 miles from Flint to Grand Rapids to find his father, Herman E. Calloway. Along the way, Lefty Lewis discovers the boy and takes him in for the evening, promising to bring him to Grand Rapids the following day.
Bud identifies Herman E. Calloway as his father. Nobody believes him, but they agree to take him to a restaurant and get it all sorted out.
Bud realizes that Herman Calloway has rocks similar to those he carried around from his mother. Herman accuses him of stealing the rocks, but really the rocks are a clue to their true relationship.
Mr. Jimmy and Ms. Thomas identify Herman E. Calloway as Bud's grandfather. Bud finally feels at home in his mother's bedroom and is eager to learn how to play the trumpet and join the band.