Greg Heffley returns for another tumultuous school year, desperately trying to shed his uncool reputation. His primary antagonist is his older brother, Rodrick, an aspiring heavy metal drummer whose main goal in life is to torment Greg. Their mother, Susan, desperate to force the brothers to bond, implements a strict bribery system called "Mom Bucks," rewarding them with cash for spending quality time together. Naturally, this scheme backfires spectacularly, leading to endless scheming and retaliation.Greg’s social ambitions are further complicated by his relentless pursuit of Holly Hills, the new girl in school. Eager to impress her, Greg makes a series of disastrous miscalculations, including accidentally wearing a pair of women’s fashion jeans to a roller-skating party. To make matters worse, Rodrick catches Greg in this humiliating moment and records it on video, turning the footage into the ultimate weapon of blackmail.As the brothers navigate their mother's constant meddling, Rodrick prepares for an upcoming talent show with his band, Löded Diaper. Desperate to keep the embarrassing video hidden, Greg is forced to wait on Rodrick hand and foot, acting as his personal servant. Despite Greg’s compliance, Rodrick threatens to leak the tape anyway, driving a massive wedge between Greg and his loyal best friend, Rowley Jefferson, whom Greg inadvertently alienates in his obsessive quest for popularity.Eventually, Susan discovers the blackmail tape and grounds Rodrick, banning him from the talent show. However, Greg’s empathy kicks in. Realizing how much the performance means to his brother—and recognizing that Rodrick secretly defended him against bullies earlier—Greg smuggles Rodrick out of the house. During the talent show, Löded Diaper’s audition goes completely awry, but a viral video of Susan enthusiastically dancing to their chaotic music unexpectedly steals the spotlight.The aftermath of the talent show brings unexpected healing to the Heffley household. The viral video inadvertently makes Rodrick and his band underground legends at school, improving Rodrick’s mood and drastically reducing his desire to torment Greg. Meanwhile, Greg learns a humbling lesson about the
superficiality of popularity and the enduring strength of sibling bonds. He manages to reconcile with Rowley, accepting that true friendship and family support are far more valuable than trying to fit in with the cool crowd. Greg steps into the next phase of the school year with newfound maturity, ready to face whatever
middle school throws his way without losing his authentic self in the process.