An FBI agent, Malcolm Turner, goes undercover as Big Momma, a large and eccentric woman, to protect a potential witness and catch a dangerous criminal. As he stays with the witness and her young son, he must navigate the challenges of being a woman while trying to solve the case.

After witnessing a murder, an FBI agent and his stepson go undercover at an all-girls performing arts school, with the agent disguised as a large, elderly woman. Together, they must navigate the world of ballet and teenage drama to solve the case.

FBI agent Malcolm Turner goes undercover as Big Momma, a nanny in a wealthy family, to find a computer virus that could endanger national security. While dealing with the challenges of impersonating a woman and taking care of the family's children, Malcolm must also uncover the identity of a rogue cop. Hilarious situations ensue as Big Momma tries to balance her undercover job with her personal life.