Max introduces himself by saying that he didn’t have a brain until he met Freak and they became Freak the Mighty together. Years ago, when Max first went to daycare, he was known as “Kicker” because he’d kick people. Max’s caregivers, his grandparents Grim and Gram, thought that daycare would be good for Max—but all it did was give Max his first glimpse of Freak, whom he remembers as looking “fierce.” Freak wore metal braces on his legs and he would hit other kids with his crutches. Years later, Freak taught Max that it’s possible to remember anything, whether it happened or not. Max definitely remembers a time when he overheard Grim saying that Max doesn’t just like “him”—Max is like “him” and so Max might hurt them. Gram shushed Grim and he pointed out that Max had big ears. Max inspected his ears to see if that’s what made him look like “him”—like Kenny, Max’s father.
The summer before eighth grade, Max is growing an inch a day and he can barely keep track of his feet. When he gets bored in his basement bedroom, which he calls the “down under,” he heads out of the house. Outside, he sees Freak, who is less than three feet tall, ordering movers around. When Freak notices Max, he points a crutch at Max and orders the “earthling” to announce himself. Terrified, Max runs back to the down under. After thinking for a while, Max goes back outside to spy on Freak. He sees Freak in the backyard, trying futilely to get something out of a tree, but he isn’t tall enough to reach even when he stands in a wagon. Max walks over and he plucks a tiny colorful thing out of the tree. Freak explains that it’s an ornithopter, a mechanical bird. They play with the bird until its rubber band breaks, and then Max pulls Freak’s wagon to his house and they go into the down under. Freak tells Max all about King Arthur and why he calls his mom, Gwen, “Gwen of Air”—it’s a play on the lady Guinevere from Arthurian legend. He explains that knights were the first robots and Max tries to hide the fact that he hates to read. The boys hear Gwen calling for Freak, and when she sees Max, she hurriedly whisks Freak away.
Later, Gram tells Max that Gwen called—Gwen feels bad for offending Max and she wants him to come for dinner. Max says that he knows Gwen was just scared of him, but Gram insists that Gwen isn’t scared of him. Max grudgingly agrees to go. Gwen apologizes and she says that Max looks just like Kenny, his father. Max tells the reader that it’s only a big deal that he looks like his father because Kenny is in prison and everyone knows what he did. That night, dinner at Freak’s house is fun; when Max gets home, he cries with happiness. A few days later, Grim and Gram agree that Max can go with Freak to watch the Fourth of July fireworks. They seem concerned that someone will step on Freak, but Max says they really need to watch out for the beer drinkers. Max is right: the local bully Tony D. drunkenly tries to torment Max and Freak. During the fireworks, Max lifts Freak onto his shoulders so that he can see. Freak remains there after the fireworks, and when Tony D.’s friends chase them, Freak steers Max into the local pond to escape and he flags down a cop car. The cops help free the boys, and Freak tells the cops that they’re “Freak the Mighty.” Back at home, Grim behaves oddly and he offers Max a cup of coffee. He commends Max for rescuing Freak, but Max tells the reader that Freak’s brain is what actually rescued him.
For the rest of the summer, Freak wakes Max up every morning so they can go on quests. One day, Freak announces a quest to the far East. He rides on Max’s shoulders for miles, through a ritzy neighborhood that, according to Freak, is full of castles. They reach the “fortress”—the hospital—and there, Freak explains that he comes to the medical research center every few months. They’re fitting him for a bionic body transplant. Max finds this extremely disturbing, but he can tell this is important to Freak. Later that summer, Freak announces another quest to find treasure—but they must conduct this quest at three a.m., as the treasure is in a storm drain and it’s a secret. Max grudgingly accompanies Freak to the storm drain and he helps Freak fish out a purse that Tony D. stole and threw down there. They find an ID for a woman named Loretta Lee. Loretta Lee’s address is across the millpond, in the tenement buildings that everyone refers to as the New Testaments. Max isn’t supposed to go there, but Freak insists that they have to in order to complete their quest. When they reach the apartment, the door opens before the boys even knock to reveal a thin blond woman and a huge tattooed man. The woman is Loretta Lee, and Max knows they’re in big trouble: the man is Iggy Lee, the leader of a scary biker gang. Iggy tries to intimidate Max and Freak until Loretta realizes that Max is Kenny Kane’s son. Iggy doesn’t believe that Kenny will be in prison for life and he doesn’t want Kenny to hear that he messed with Max, so he lets Max and Freak go.
Max feels a sense of dread as school approaches. The adults decide that it would be good for Freak to have a helper, so Max is going to attend Freak’s classes instead of the “learning disabled” classes. Things go fine until English, when Mrs. Donelli tries to get Max to speak in front of the class. Kids taunt Max until Freak and Max become Freak the Mighty. Max feels proud, and Freak leads the class in a chant of “Freak the Mighty!” Mrs. Donelli sends them to the principal’s office. Mrs. Addison seems charmed by Freak and she lets the boys go. In October, Max learns that the hype surrounding Friday the 13th is real. Though school has been going well—Freak has taught Max to read, though Max still insists he can’t write—Max receives a disturbing summons to Mrs. Addison’s office. He’s convinced that she’s going to put him back in the learning disabled classes but instead, she tells him that Kenny is getting out on parole. Max screams that he doesn’t want to hear it, covers his ears, and curls up in the corner. When he comes to, the nurse is crying, so Max believes that he hurt her and doesn’t remember it. Mrs. Addison assures Max that she won’t make him see Kenny. Then, at lunch, Freak stops breathing and he has to go to the hospital. When Mrs. Addison tells Max that he’s had quite the day, Max points out that Freak is the one who had the bad day. Mrs. Addison says that Max is going to be okay.
Things go back to normal until right before Christmas, when Max hears Grim and Gram shouting, which they never do. Gram insists that Grim cannot get a gun since Kenny might break in, steal it, and shoot them all. Gram thinks the police will protect them, but Grim points out that they couldn’t protect Annie. Later, Grim talks privately with Max and he says that since Kenny is out on parole, he took out a restraining order so that Kenny can’t get near the house. Max suggests that Grim get a gun no matter what Gram says, but he agrees to stay near the house for a few days. Gwen and Freak join Grim, Gram, and Max for Christmas Eve. It’s a wonderful evening until Max wakes up in the middle of the night to a cold wind and a huge hand on his face: it’s Kenny. Kenny kidnaps Max, who’s terrified. Max thinks that Kenny doesn’t need armor—he’s strong enough to get whatever he wants just like he is. Kenny leads Max to Iggy and Loretta’s apartment in the Testaments. He menacingly scolds Iggy for allowing Loretta to drink and he forces Iggy to make him and Max burgers. Max can tell that Iggy is terrified.
Iggy then takes Max and Kenny to the apartment of an old lady who’s out of town for the holidays. Max makes the mistake of looking at the door, which encourages Kenny to tie Max up. Kenny and Max sleep for a while, but Kenny later wakes Max up and he says that he didn’t kill anyone; people just assume he’s cruel because he’s big. He says that Grim and Gram are awful people for getting him locked up and keeping him from seeing Max, and he swears on a Bible that he didn’t kill Annie, Max’s mother. Max stays up the rest of the night, trying not to remember horrific things. In the morning, Kenny snaps awake when Loretta brings them cold pizza. When they see a cop car go by, Kenny decides that they need to hide elsewhere while Iggy procures a gun and a car for them. Kenny leads Max to a burned-out building, helps him down the slippery stairs, and ties Max to an old boiler while he goes to find Iggy. Max thinks he sees and hears things, but then Loretta Lee stumbles down the stairs to free Max. She manages to cut the ropes binding Max’s hands and feet, but Kenny appears out of nowhere and chokes her. Max feels like he’s four years old again and watching Kenny kill Annie. He tries to hit Kenny and screams that he remembers Kenny murdering Annie. This distracts Kenny; he starts to choke Max instead.
Just then, Freak bursts in through the basement window with a squirt gun and he shoots Kenny in the face with what he says is sulfuric acid. Max scoops up Freak and they race out of the building, where they find police officers and Iggy Lee. The cops arrest Kenny and they get Loretta to the hospital. Max has to tell his story over and over again at the police station, and he dreads having to eventually testify. When school starts again, Mrs. Donelli puts up the photo of Max and Freak that ran in the papers on the bulletin board. Freak asks her to leave it up even though someone draws moustaches on them. Max ends up not having to testify; Kenny pleads guilty to all charges and he will be in prison for a long time. Despite this seemingly happy ending, Max still fears that he’s going to grow up to be just like Kenny.
Freak’s birthday party happens right after school lets out for the summer. It’s a double birthday, as it’s also Freak the Mighty’s first birthday. Due to Freak’s declining health, the party is a small affair. Freak receives a computer that will allow him to go to school over the phone, which confuses Max—he knows that Freak is going to receive a bionic body and so he’ll never have to miss school. During the party, Freak has a seizure and he’s taken to the hospital. Max can’t bear to leave Freak alone so he walks to the hospital the next day with the ornithopter. Gwen and Dr. Spivak allow Max to briefly see Freak. Freak seems smaller than ever and he’s connected to all sorts of tubes and monitors. Freak gives Max a blank book and he asks Max to record Freak the Mighty’s story in it; he’s going to get his bionic operation tomorrow and so he won’t have the time to write it himself. The next day, when Max returns to the hospital, he realizes that Freak died overnight. Max loses control and he breaks through several glass doors before the cops finally catch him. Dr. Spivak sits with Max, and Max tells him about how Freak spoke about his bionic operation. Max believes at first that Dr. Spivak lied to Freak about the operation, and then that Freak lied to Max about the operation. Dr. Spivak tells Max that Freak probably told the story to give himself hope; he’s known for a long time that he wouldn’t live long.
Max wallows in grief for months. Around Christmastime, he runs into Loretta Lee. Loretta says that Gwen now lives in California with a new boyfriend. When Loretta learns that Max is doing nothing, she points out that doing nothing is a drag. This makes Max think, so he pulls out the blank notebook that Freak gave him. At first, Max thinks he can’t write—but he starts recording Freak the Mighty’s story and he keeps writing until spring. Now, having written the story, Max feels okay remembering things and he thinks he might even read some books.
