Lt. Shane Wolfe (VIN DIESEL) is a Navy SEAL who's been trained to deal with most any situation he might encounter while serving his country. That includes rescuing Howard Plummer (TATE DONOVAN), a kidnapped government scientist who's developed a satellite program that could prevent any country from launching their nuclear weapons. Yet, when Shane lets down his guard by allowing Howard to call home while still in hostile environs, the scientist is assassinated and Shane is wounded.
Two months later, Shane is ready to return to his normal SEAL duties, but Capt. Bill Fawcett (CHRIS POTTER) informs him of a new mission. While he accompanies Howard's widow, Julie (FAITH FORD), overseas to open a safe-deposit box that may contain the missing satellite program, Shane is to protect her five kids and see if the program might be hidden somewhere inside the house. Considering his background and the fact that the family's nanny, Helga (CAROL KANE), is still there, Shane figures this will be an easy assignment.
Yet, his training hasn't prepared him for the teenage attitudes of Julie's oldest kids, Zoe (BRITTANY SNOW) and Seth (MAX THIERIOT), dealing with their younger siblings, Lulu (MORGAN YORK) and Peter (KEEGAN & LOGAN HOOVER), or the prospect of changing Baby Tyler's (BO AND LUKE VINK) diaper. The kids balk at his strict rules, Helga eventually leaves, and the neighbors, Mr. and Mrs. Chun (DENIS AKIYAMA and MUNG-LING TSUI) don't approve of the loud and obtrusive security devices he's installed at the house.
Things aren't any better at school. While Principal Claire Fletcher (LAUREN GRAHAM) allows him to be there to protect the kids, Vice Principal Murney (BRAD GARRETT) -- who actively dislikes Seth, particularly when he quits the wrestling team -- is another matter. As he tries to deal with him and come to some sort of agreeable arrangement with the kids, Shane tries to find the missing satellite program, all while dealing with a pair of masked ninjas who are looking for the same.