FBI agent Malcolm Turner (played by Martin Lawrence) is filled with pride upon discovering that his stepson, Trent Pierce, has landed a spot at Duke University. However, Trent's ambitions go beyond academics; he's been sneaking around as the rapper Prodi-G and wants Malcolm to sign a recording contract for him, even though he's underage. When Malcolm declines, Trent's friends incite him to execute a scheme during one of Malcolm's work shifts to get the crucial signature he desires.
As this unfolds, Malcolm is undercover, masquerading as Canetti, to deliver what appears to be an important flash drive to Russian mobster Chirkoff. Unfortunately, Canetti discloses that the drive is a blank, and the real information is concealed with a friend at the Georgia Girls School for the Arts. During the meeting, Canetti's cover is blown, leading to his tragic death, witnessed by Trent.
In a frenzy, Malcolm jumps into action to save Trent, but he realizes that Chirkoff's crew will be right behind them. To evade capture, they disguise themselves as Big Momma, the grandmother of Malcolm's wife Sherry, and her great-niece Charmaine—a larger young woman enrolled at the arts school.
Embracing her role as a house mother at the elite school, Big Momma faces new challenges as Trent strives to maintain his cover among the attractive student body. His closest confidante becomes Haley Robinson, with whom he unexpectedly connects. In the midst of this, the headmistress announces a theft of a priceless music box from the library, which Malcolm suspects may contain the vital flash drive.
On a mission to investigate the library, Big Momma encounters Kurtis Kool, a charming security guard who offers to show her around—unaware that she is actually Sherry’s grandmother incognito. As Malcolm notices a photo of Kurtis with Canetti, he starts to piece together the mystery entwined with the music box and is determined to unveil the truth.
As tensions rise, Trent becomes increasingly entangled in the deception. His friends are pursued by gang members posing as record producers, compelling them to disclose his location. Things get complicated when Trent plans a date with Haley, only to face an unexpected surprise that threatens to expose his secret.
Amidst Trent's mentorship to Haley, where he assists her in honing her musical skills for a prestigious "Showcase" event, their relationship deepens into a romantic nature culminating in a heartfelt kiss. Encouraged by Haley to embrace educational opportunities, Trent cleverly evades capture just before the gang can nab him.
With Malcolm trying to win over Kurtis through insincere charm, their strategy backfires, leading to the revelation of an illicit exchange regarding a stolen mascot from a rival institution. This critical moment leads to Malcolm disclosing his true identity to Kurtis, a major turning point in their dynamic.
As Trent's support enables Haley to find her self-confidence, she reveals her motivations for stealing the music box stemmed from her desire to join the school's elite group, the "Divas." Driven by ambition, Haley prepares to step into the spotlight with Trent as Charmaine. However, things take a turn when Malcolm has to intervene, forcing him to preserve his disguise and awkwardly participate in the performance.
The act spirals into chaos as Trent loses focus and breaks character, infuriating Haley who storms off the stage, just as gang members arrive to heighten tension with a thrilling chase.
Trent's miscalculation brings undue attention to himself as he tries to explain his actions to Haley. In a fortunate turn, he manages to retrieve the all-important flash drive just in time, but his distraction allows the gang to catch up and confront him at gunpoint. With a bold move, Big Momma steps in, enabling a daring escape, only for the trio to be recaptured, finally unveiling Malcolm's disguise.
As everything hangs in the balance, Kurtis makes a timely entrance with a taser, diffusing the crisis and making a daring save. In the aftermath, Trent and Haley mend their relationship, while Malcolm reluctantly signs Trent's contract, which Trent quickly tears up in favor of focusing on higher education.
In a heartfelt ending, Malcolm and Trent agree to keep their wild escapades under wraps from Sherry, signaling the start of a new journey for them both.
