Ace undercover cop Malcolm Turner (Martin Lawrence) is none too pleased when he finds out his son Trent (Brandon T. Jackson) wants to be a rapper rather than attend college. The argument becomes a moot point, however, when Trent witnesses a murder carried out by vicious Russian criminal Chirkoff (Tony Curran).
Needing to hide Trent in a hurry, Malcolm falls back on his old Big Momma disguise and browbeats his son into disguising himself as 'Charmaine Daisy Pierce', the supposed niece of his alter ego.
Enrolling Trent in an all-girls school, Malcolm must prevent their cover from being blown, but the young man's feelings for classmate Haley (Jessica Lucas) threaten to expose them to the gangsters who are hot on their trail.