Thirteen-year-old Chase Ambrose wakes up in the hospital with no memory. His mother Tina, college-aged brother Johnny, and doctor inform him that he has developed amnesia due to a concussion: he likes to sit on his roof, and one day he fell off. When the doctor asks Chase whether he can remember anything, he only recalls a little blond girl. Tina and Johnny take Chase home, where his father Frank is waiting to greet him. When Frank gives Chase a noogie, Tina and Johnny explain that Chase has a concussion and can’t play football on his doctor’s orders. Frank, undeterred, insults the doctor and praises Chase’s toughness.
Shoshanna Weber messages her twin, Joel, to let him know that Chase—who bullied Joel so badly that the Webers sent him to boarding school—fell off a roof and just left the hospital. Though Shoshanna is hoping to cheer Joel up, he’s miserable at his new school. The day before school starts, Shoshanna runs into Chase at a frozen yogurt shop. When he smiles at her, she upends her frozen yogurt on his head and runs out.
On the first day of school, the football players who were Chase’s closest friends, Aaron Hakimian and Bear Bratsky, take Chase aside. When Chase explains that he has amnesia, they seem suspicious and worried. The principal, Dr. Fitzwallace, summons Chase to his office and advises Chase to take advantage of his “fresh start,” but Chase keeps hanging out with Aaron, Bear, and the football team. One day, Aaron and Bear mention having to do community service at an assisted living facility; Chase learns that all three of them were sentenced to community service for hiding cherry bombs inside Joel’s piano during a school recital, though Chase doesn’t have to go anymore because he’s received a medical exemption.
Brendan Espinoza is filming cliques in the cafeteria when Chase comes to sit with him. Brendan’s terrified because Chase and his friends have bullied him in the past—but it quickly becomes clear that Chase has amnesia and is much more polite now. When Brendan can’t get other video-club club members to help him film a video, he asks Chase for help. After Chase agrees, Brendan realizes Chase is excellent with a camera and invites him to join video club. When Chase shows up at a meeting, all the members but Brendan are horrified—none more so than Shoshanna. After making her displeasure known, she expresses a desire to enter the National Video Journalism Contest, which will require entrants to interview a senior citizen.
After filming a Saturday football scrimmage for video club, Chase goes to interview the football players in the locker room, where he has such an unexpectedly pleasant time that he decides to go to community service afterwards with Aaron and Bear. At the assisted living facility, Chase is fascinated by a photo he sees in one sleeping senior’s room. The photo is of the man accepting a Medal of Honor from President Truman. Later, Bear takes $20 from an elderly woman in cognitive decline who thinks she’s tipping hotel staff. Chase tries to get Bear to give the money back, but he won’t. After leaving, Chase returns to the facility and slips his own $20 under the resident’s door. On his way out, he stops by the room of the man with the photo and sees a nameplate: Mr. Julius Solway. Mr. Solway asks what Chase wants. When Chase asks how Mr. Solway won the medal, he responds sarcastically but then explains it was during the Korean War.
Kimberly Tooley, who has a crush on Chase, sees him shove a bully into a wall for getting rough with Brendan. When Brendan and other video club members thank Chase, Shoshanna reminds them about what Chase did to her brother. After they disperse, Chase admits to Kimberly that he can’t remember Shoshanna’s brother. Ecstatic that post-amnesia Chase is talking to her, Kimberly joins video club. Brendan immediately develops a crush on her, but his attempts to impress her fail.
Aaron is upset that Chase has amnesia. He wants his old friend back, but in addition, Chase is in possession of a valuable object that he, Aaron, and Bear were supposed to split three ways. Aaron wants to ask Chase some questions at community service, but Chase is too busy helping seniors and chatting with Mr. Solway about the Korean War. Chase learns that Mr. Solway won his Medal of Honor for opening an enemy tank and throwing a grenade inside. Mr. Solway admits he can’t remember throwing the grenade; the violent aftermath was so horrible that his brain repressed it. He also tells Chase that he lost the medal at some point.
At a video club meeting, Shoshanna is explaining how good the National Video Journalism Contest entries could be if entrants found the right seniors to interview. Chase suggests Mr. Solway. Shoshanna is suspicious but intrigued. She goes to the assisted living facility to meet Mr. Solway. Mr. Solway blows her off until Chase walks in with snacks. When Mr. Solway realizes Chase knows Shoshanna, he agrees to help with “their” project. Chase and Shoshanna have been interviewing Mr. Solway for three days when Shoshanna starts trying to find mementos they can film. At the back of Mr. Solway’s closet, she finds the empty case for his Medal of Honor. Walking home from the facility, Shoshanna mentions to Chase that it’s weird of Mr. Solway to stash his medal at the back of his closet. Abruptly, Chase guesses that the medal was stolen and the box was put in an out-of-the-way place to hide the theft. Because Bear took money from Mrs. Swanson, Chase wonders whether Bear and Aaron are the thieves.
Though it makes Shoshanna uncomfortable, she can’t deny that post-amnesia Chase is a different, nicer person. One day, Shoshanna’s mother spots Shoshanna and Chase working together. She drags Shoshanna home, where she and Shoshanna’s father stage an intervention over Shoshanna befriending Joel’s bully. Shoshanna argues that they should bring Joel back from boarding school: the Webers only sent him away because of Chase’s bullying, and Chase isn’t a bully anymore. The Webers, though nervous, decide to bring Joel home.
When Chase and Shoshanna finish their video, the school holds an assembly to watch it. Aaron and Bear are furious: Aaron thinks Chase is boasting about being a stand-up guy, while Bear thinks it’s suspicious that Chase chose Mr. Solway to interview. Aaron suggests they show Chase who “his real friends are.” Later, Joel and Kimberly are helping Brendan film a video in the music room when Aaron and Bear burst in with fire extinguishers, spraying the other kids with foam. They claim Chase sent them to attack Joel. Kimberly runs to get Chase; when she returns with him, he and Bear fight over a fire extinguisher—and when Chase wins, he accidentally hits Joel in the face with it.
Teachers arrive. Aaron, Bear, and Chase are taken to Dr. Fitzwallace’s office, where Aaron lies that the video equipment started a fire in the music room—he, Bear, and Chase were helping. Chase realizes that no one will believe he wasn’t bullying Joel. When Dr. Fitzwallace asks Chase to confirm Aaron’s story, he begrudgingly lies to save himself. Dr. Fitzwallace doesn’t punish the boys—but Chase is kicked out of video club, and all the club members but Brendan now believe Chase’s nice-guy amnesiac personality is an act. Meanwhile, a questionable doctor Frank found has cleared Chase to play football. One day at football practice, Chase gets into a big fight with Aaron and Bear and accuses them of stealing Mr. Solway’s medal. Aaron, flabbergasted, reveals that Chase stole the medal, though the three boys planned to split the value three ways. Chase asserts that he’ll give the medal back if he finds it, but Aaron claims that he and Bear have a right to two-thirds of the medal’s value.
When Brendan tries to make another video, he discovers that the camera contains footage of the music room fracas proving that Chase hit Joel by accident. He urgently texts Chase, Shoshanna, Joel, and Kimberly to come to his house the next morning. As Chase leaves for Brendan’s, he sees movers hauling stuff out of his neighbors’ house, including a painting depicting the little blond girl he remembers. When he asks his neighbor about the painting, she tells him that it used to hang in an upstairs room in her house. Chase climbs onto his own roof to find the spot from which he must have spied the painting—and discovers Mr. Solway’s Medal of Honor up there.
When Chase doesn’t show up at Brendan’s, Brendan screens the footage he found for Shoshanna, Joel, and Kimberly. Brendan calls Chase’s mom and discovers he left for the assisted living facility. The kids decide to find Chase there. At the facility, Aaron and Bear spot Chase with the medal and try to grab it. After Shoshanna, Kimberly, Joel, and Brendan enter Mr. Solway’s room, Shoshanna and Kimberly spot Chase running down the hall toward them—only to see Aaron knock Chase down and Bear start hitting him. Shoshanna and Kimberly drag Bear off Chase; when Bear shoves the girls, Brendan jumps to their defense. Eventually, the facility authorities show up and call the police.
Chase, who has taken sole responsibility for stealing the medal, stays at home, full of self-loathing, until his juvenile court date. His hearing is packed with community members. To his great surprise, not only his mother and father—who unexpectedly praises Chase’s new, less sports-obsessed personality—but also Shoshanna take the stand as character witnesses in his defense. It turns out everyone is there to speak in amnesiac Chase’s defense. When the judge asks Chase whether he can promise he won’t return to his pre-amnesia self, Chase realizes he could lie—but he decides to be scrupulously honest and says he can’t promise that. The judge is about to sentence Chase when Mr. Solway bursts in with his Medal of Honor and claims that Chase never stole the medal—Mr. Solway lent it to him. The judge doesn’t believe Mr. Solway, but he decides not to punish Chase. Everyone celebrates jubilantly.
Chase becomes a football player and a video club member. Kimberly starts dating Brendan because she appreciates his bravery in standing up to Bear during the fight at the assisted living facility. She also uploads a YouTube video of Brendan wearing a tuba while covered in fire extinguisher foam, which, to Brendan’s great delight, goes viral.
