Sixteen-year-old Nicholas Andreas is called before a judge after his girlfriend, Caitlyn, seeks a restraining order against him. She claims that Nick beat her, but he insists he only slapped her once when she provoked him during an argument. The judge grants Caitlyn's request and orders Nick to attend counseling for anger management. He must also write 500 words a week in a journal about his relationship with Caitlyn.
Nick begins the journal with the story of how he met Caitlyn. He and his best friend, Tom, spotted her walking into school at the beginning of their sophomore year. Nick thought she was a new girl. Tom explained that they'd known her since kindergarten, but she'd lost weight over the summer. Although Nick was one of the popular kids in school, he had no self-confidence and was afraid to talk to Caitlyn.
After writing this entry, Nick begins the Family Violence class. The instructor, Mario, demands honesty, punctuality and courtesy from the students. If they fail to meet his requirements, they can be ordered to take the class again or be put in jail. Mario's biggest rule is that the participants take responsibility for their actions and not blame their girlfriends, alcohol or drugs for their behavior. One of the students breaks down, confessing he doesn't know how to be honest and reveal the pain he hides inside. Nick also tries to block out a scene starting to play in his mind. He's afraid he might break down as well. When Mario confronts Nick about why he has to take the class, Nick admits that he slapped Caitlyn because they were arguing. He tells Mario that his life has been ruined because of this misunderstanding. No one in school will speak to him, including Tom, his best friend since kindergarten.
Later, Nick writes in his journal about how Tom set him up with Caitlyn. She agreed to go to a classmate's party with him that weekend. Nick alludes to being jealous of Tom's relationship with his parents; Nick's relationship with his own father is strained. In fact, Nick's father sells Nick's car without telling him, even though it had been given to him as a birthday present.
At school, Nick is treated like a pariah. Former friends circle around Caitlyn any time he happens to pass her in the hall. Others write disparaging remarks about him on the blackboard, trying to provoke his anger. Instead, Nick uses his journal to reflect on his relationship with Caitlyn. He reminisces about their first date. When uninvited thugs crashed the party they attended and started trashing the house, Caitlyn spoke up to make them stop. One of the boys made a lewd comment and touched her waist, sending Nick into a frenzied rage. He pummeled the boy until Tom pulled him away. Caitlyn rewarded Nick with a kiss for defending her honor. When one of her friend's irritated Nick, he demanded that Caitlyn no longer hang out with her. After a brief argument, Caitlyn agreed.
When the subject comes up in the Family Violence class, Mario tries to help the students see that isolating a girlfriend from her family and friends is an example of a controlling behavior that he hopes to teach them to overcome. Mario also informs them that at the next class, they will be talking about their relationships with their parents. Nick senses the others have the same fears he does about this subject. He writes in his journal about how his father punched him in the face when he discovered Nick had tricked the maid into buying him beer for a party. He had to stay home from school the next day so no one would see the bruise. He phoned Caitlyn to tell her he was sick and then argued with her when she wanted to stop by his house. He also became irate when she didn't immediately agree to stay home from the football game that night, calling her foul names. They made up when she agreed to stay home. The following day Caitlyn insisted on visiting him, pushing past the maid and pounding on Nick's door until he let her in. She realized his dad beat him and tried to convince Nick to tell a teacher or the police. Nick refused the advice but accepted her gentle hugs. He confessed he loved her, and she told him the same.
Nick disobeys the court order by calling Caitlyn and hanging up without speaking. He also conspires to meet with her in the halls at school. When he catches her alone one day, he tries to make her remember how good they were together and asks her to drop the charges against him. When she hesitates, his temper rises, and he tells her he never loved her. She is able to face him down at that moment and thank him for reminding her why she can't be with him.
In Family Violence class, Nick manages to avoid the subject of his father's abuse, telling the group that he and his father get along fine. They had been together, just the two of them, since his mother left when he was 5. Others in the group describe childhoods embroiled with psychological and physical abuse. Nick makes friends with Leo, one of the other members of the class. Leo eventually convinces his girlfriend, Neysa, to drop the assault charges against him and take him back so he doesn't have to attend the group anymore.
Nick continues to write about his relationship in his journal, admitting to himself how he manipulated Caitlyn by calling her fat or threatening to break up with her if she did anything he didn't like. He psychologically controlled her, demanding she do only the things he gave her permission to do. But he could also be kind to her, such as when he rescued her from an initiation that turned mean.
Although Leo no longer has to attend Family Violence class, he and Nick hang out together. Leo gets Nick to admit that his dad sometimes hits him. Leo shows Nick a gun he keeps to threaten his mother's boyfriend. The man psychologically abused Leo, his mother and his brother.
The incident scares Nick, and he writes his thoughts in his journal, trying to work out if he could ever be as violent as Leo. He realizes his abuse of Caitlyn escalated when they went on a trip with friends to Key West. She tried to confront him about his behavior on the drive home, and he became blinded with rage, threatening to drive their car off a bridge and into the water. When she grabbed the wheel to straighten out the car, he hit her in the face. After that weekend, Caitlyn tried to break up with him, but Nick convinced her to give him another chance.
A couple of Nick's old friends pull him aside in the hallway and hit him, telling him to stay away from Caitlyn. His English teacher sees the bruises and questions Nick. She's noticed his absences and bruises before, but Nick won't admit to his father's abuse. She tells him not to consider himself a bad person because of what he did to Caitlyn, intimating that she knows he has issues he needs to deal with and that, being only 16, he has time to redeem himself.
At counseling, Mario pushes Nick into admitting the emotions he felt before he hit Caitlyn. When Nick shuts down, Mario goads him into getting angry, even telling Nick to hit him. Nick gets mad, but still won't hit Mario. The counselor explains that Nick has to behave in a similar way around women. Instead of thinking he can bully his girlfriend into behaving, or beating her when he's angry with her, Nick has to learn to walk away from the situation. That afternoon, Nick meets up with Leo and Neysa to work at a carnival for school service hours. The three work the concession stand together. Nick gets an uncomfortable look in the proverbial mirror as he watches Leo psychologically abuse Neysa during the afternoon. When the night is over, Nick makes plans to stay away from Leo.
During the next Family Violence class, Mario paces the room and reacts with a short fuse when students question him. Nick can see Mario is upset about something but won't tell the class about it. His receptionist comes in and whispers something about Leo and the newspapers. Mario leaves the class, telling them to read their workbooks. At the end of class time, the rest of the students leave, but Nick stays behind. Mario returns and explains that Leo killed himself and Neysa. The news devastates Nick. He races home, trying to deal with the emotions swirling inside him. He takes out his journal and writes about his last fight with Caitlyn. She'd gone against his wishes and performed in the school talent show. He was so insecure that he thought she sang the love song to someone else in the audience, not him. Enraged, he dragged her to the parking lot and began beating her until Tom finally broke them apart and hit Nick in the jaw.
Reliving his abuse of Caitlyn in light of Leo's tragedy starts Nick on the road to real recovery. On their last day of class together, Mario admits that he was once an abuser. He beat his wife to drown out the voice of his father telling him he was a loser. When he pushed her out of a moving car, he was forced to attend the same class. He repeated the class until the lessons stuck and he learned how to drown out his father's negative voice in his head. Nick tells Mario that he's learned that being a man isn't about having the most power, but in taking responsibility for your actions and doing the right thing even when no one is looking. When the session is over, Nick asks if he can take the class again. Mario agrees. Nick also leaves his journal for Mario to read. That night, when his father tries to hit him, Nick stands up to him.
On his first day back to school for his junior year, Tom stops Nick in the parking lot. He tells Nick that Caitlyn has moved away. Before she left, she told him about how Nick had been abused by his father. Tom can't understand why Nick never told him about it. She also told Tom that after her last phone conversation with Nick, she believes he truly has changed. Nick and Tom forgive each other — Nick for keeping secrets and Tom for shutting his friend out the year before. The school year starts on the hopeful note of their renewed friendship.