At the beginning of the school year, middle school student Greg Heffley begins writing in a journal to document his daily life. Greg complains that he is stuck in middle school with a bunch of “morons” and that he’s only writing in this journal because he’s sure he’ll be rich and famous one day and he doesn’t want to have to answer stupid questions. Greg thinks he is better than his classmates, but he also acknowledges that he isn’t the most popular student. Greg decides to focus on gaining popularity, and as the school year progresses, Greg rolls out one scheme after another in hopes of finally earning a name for himself as a popular kid.

At home, Greg has to deal with his very traditional dad, his protective mom, his obnoxious older brother Rodrick, and his baby brother, Manny. Amid the chaos of his home, Greg often leaves his house to find peace, and he spends a lot of time with his best friend Rowley Jefferson. Greg complains that Rowley is uncool and doesn’t seem to care about popularity the same way Greg does, and Greg often blames Rowley for getting in the way of Greg achieving popularity. Still, Greg is perfectly content to use Rowley to get what he wants, and he enjoys playing jokes on Rowley.

In January, Greg breaks Rowley’s hand in a freak Big Wheel accident, but he takes no personal responsibility for his actions. When Rowley has to start wearing a cast, Greg grows jealous of the attention Rowley is getting at school. In February, Greg and Rowley try to become cartoonists for the school newspaper, but Greg is so obsessed with controlling the project that he drives Rowley away. In March, while serving on the school’s Safety Patrol, Greg abuses his power and terrorizes a bunch of kindergarteners. Instead of owning up to his mistake, however, Greg lets Rowley take the fall for his actions, and Rowley decides to stop speaking to Greg. As the school year draws to a close, Greg realizes that Rowley is becoming far more popular than him, and all of Greg’s attempts to get attention at school have backfired.

One day, Greg and Rowley are cornered by the same teenagers that attacked them on Halloween night, and Rowley is forced to eat a moldy piece of cheese that has been sitting on the school’s blacktop for over a year. Greg knows that Rowley’s reputation will be ruined if anyone finds out what happened, so he takes the fall for Rowley and tells everyone in school that he threw the Cheese away. Greg becomes a social outcast because everyone believes he has the “Cheese Touch,” but Greg doesn’t mind. In the end, Greg and Rowley become friends again, and Greg realizes that being popular isn’t worth the hassle. He decides he would rather have Rowley’s friendship, and he can always remind Rowley of what really happened to the Cheese.