Six years after meeting her during an investigation, FBI agent Malcolm Turner is now married to Sherry Pierce and is the stepfather of her son Trent, and assumes a desk job to be close to her as they await the arrival of their first child.

He learns that he was investigating former military intelligence specialist Tom Fuller, who now works for the National Agenda Software corporation, and had discovered he was creating a computer worm that could provide backdoor access to government databases.

Discovering Morales is sending an agent undercover to secure the job of nanny within Tom's family, Malcolm decides to take advantage of this, lying to Sherry that he must go out-of-state for a conference.

Malcolm retrieves the disguise he used while impersonating Sherry's grandmother - known affectionally as Big Momma - and secures the nanny job by exposing flaws in the other candidates.

After Leah threatens to fire Big Momma for her handling of her chores, Malcolm spends the night doing all of the work and successfully wins back her favor.

Soon after, men working for Agenda's CEO Casal take both of them hostage in order to coerce Tom to assist in a business deal involving the computer worm.

While the case is ended and he has made amends with Sherry, Malcolm decides to stay in California a while longer in order to assist Carrie, after helping her team improve themselves for an upcoming cheerleading championships.

Helping them to successfully win, Malcolm departs, leaving behind a letter from Big Momma bidding farewell to the Fullers and hints that their paths will cross again someday.