Fourth grade looms large for Mason Dixon. It starts tomorrow, and he is anxious. Every school year of his young life has held some sort of disaster, and this one is shaping up to be the same. For starters, Mason’s parents want him to join the Plainfield Platters, the school’s choir for fourth- and fifth-graders. Though Mason has a very good voice, he doesn’t like to sing, especially in front of lots of people. He doesn’t like to do anything in front of lots of people. Another drawback is that he has a new dog named Dog, and he’ll have to leave him at home. He shares Dog with his best friend, Brody, who lives next door. Brody’s dad is allergic to animals, so Brody can’t have Dog at his house. Brody is as exuberant about school — well, about everything — as Mason is not.
Mason’s fourth-grade teacher is Coach Joe. All his communications are in sports terms. His class is a “team,” a class meeting is a “huddle,” and he wants his team to have a winning season. Mason hates sports. Coach Joe wants his team to make a full-court press on writing, and he gives the class/team a writing assignment. They are to personify an inanimate object. Mason decides to write about a piano named Pedro who doesn’t like to play music — a very close analogy to Mason who doesn’t like to sing, especially with the Plainfield Platters in front of lots of people.
Mason’s parents insist that he participate in the Plainfield Platters for at least three months before he drops out. At the first practice on Tuesday, Mason sees Puff — a large stuffed dinosaur and the school’s mascot. Usually the mascot is kept in a display case, but now he sits on a chair next to the piano. Mason doesn’t want to sit in the front with Brody, so he ends up on the riser next to the class bully, Dunk, who shoves him off. Mason lands on the floor. The music teacher, Mrs. Morengo, moves Mason to the first row next to Brody, where he unwillingly sings, rather than mouths the words, because she is keeping an eye on him.
On Friday, because the fourth-grader’s voices are new to her, Mrs. Morengo decides to have each of them sing a short solo from the school song, “Puff the Plainfield Dragon.” Mason is sure the Puff song will be stuck in his head a long time after hearing so many repetitions. Finally, it’s his turn to sing. He is dismayed when Mrs. Morengo likes his singing and writes down the name of a voice teacher to give to his parents.
The next week, the principal announces that their school has been chosen for a special honor and that the Plainfield Platters will perform a televised concert in one week. This means that they’ll have practice every morning before the concert. Brody notices at the first concert practice that the treasured, 20-year-old Puff has some rips and suggests to Mrs. Morengo that Mason take it home for his mother to repair. He wants Puff to look good in case TV cameras zoom in on him. Mrs. Morengo agrees. Brody and Mason carry Puff home, and Mason notes how interested Dog is in Puff. He makes sure Puff is locked up tight when no one is around to supervise Dog and also warns his mother about Dog’s potential threat. But when he returns home from school the next day, Dog greets him at the door with a green dragon tail in his mouth. It seems Mason’s mother was distracted when the doorbell rang, and Dog seized the moment. The bottom half of Puff is all that remains. Mason’s mother says she will take full responsibility and call Mrs. Morengo.
Mason finishes work on his composition for Coach Joe. He has Pedro go on strike, never to play again. At the next concert practice, Mason is surprised when Mrs. Morengo says she’s decided to have one of the children dress as a live Puff and chooses Brody to be the one in costume and to sing a Puff solo. Mason is mystified to find out his own mother is the creator of the Puff costume, and she hasn’t told anyone about what happened to the beloved school mascot. To get out of singing, yet still be part of the concert, Mason asks Mrs. Morengo if he can be the stage manager in charge of lights. He is relieved when she agrees.
When Mason gets home, he talks with his mother about the concert and tells her that Mrs. Morengo was asking about Puff. Before she answers, the doorbell rings, and a big box is delivered. It’s a new Puff! Mason’s mother found a replacement Puff on eBay and ordered overnight delivery.
The night of the concert arrives, and Mason is pleased to not be singing; he told his parents that he wanted to surprise them with his role in the production. The Platters are the last group to perform. When Brody enters the stage, the audience says “Awwwwwww!” just as Brody said they would. But on his cue to sing, nothing happens. Brody freezes. Mason watches from his position on the lights, willing Brody to sing. He doesn’t. Mason finally decides to rescue his friend from disaster by walking on stage, throwing his arm around Brody’s shoulders and singing himself. Brody then joins in, and the concert concludes with the audience singing along. Afterward, Mason’s parents think the surprise was Mason’s solo — the fact that he ran the lights was a bonus. Mason concludes that maybe Pedro the piano should come out of retirement and play after all — but Mason is still not interested in voice lessons.