Greg Heffley is anxious about starting middle school but is somewhat reassured by the fact that his best friend, Rowley Jefferson, and he will be at the same school. Greg is coming to terms with this important transition but also stands in his older brother’s shadow—a position made more difficult by Rodrick’s incessant teasing and pranking. Just at the point when he most needs an older role model, Greg cannot find one in his own brother. Thus, the maturing process gets off to a slow start as Greg tries to strike out on his own but constantly thwarts his own partially formed ambitions through his selfishness and immaturity.

The reader sees—literally, in the drawings—and reads all about Greg’s awkward attempts at finding new aspects of his identity. Unlike Rowley, Greg is constantly concerned with how others perceive him and cares greatly about being considered popular. When he decides to run for a school office, Greg speculates about the increased status the position will convey and the likelihood of a particular position helping him fit in. Tellingly, he doesn't think about any leadership qualities the position might require (or whether he possesses those qualities), and the results are predictably disastrous. Greg's other attempts to gain prestige, fame, or any positive recognition likewise end in failure and occasionally threaten his closeness with Rowley. Even the sure-fire Class Clown position that Greg erroneously assumes would be his turns out not to be a sure thing.

Greg and Rowley's experiences writing their comic strip showcase all three themes, but particularly friendship. Greg initially tries to take the easy route but also dominates their shared enterprise. As Greg alternates between trying to take the easy route and criticizing Rowley’s ideas and abilities, we gain insight into his insecurities about going it alone and exposing himself to possible failure. When Rowley takes charge of the situation, Greg feels jealous and resentful—possibly this is the first time he has really seen his friend outdo him. Rowley and Greg have a falling out, but after they are both bullied by a group of teenagers, Greg realizes that friendship is more important than self-interest. In the end, Greg refuses to let others take advantage of his friend and begins to understand that their individual strengths are enhanced by their unity.