U.S. Navy SEAL Lieutenant Shane Wolfe is assigned to rescue Howard Plummer, a man working on a top-secret government project, from a group of Serbian rebels. Wolfe and his team manage to get Plummer off an enemy boat but are shot while boarding the escape helicopter. Plummer is killed in the attack, and Wolfe spends two months in the hospital. Wolfe's commanding officer, Captain Bill Fawcett, is assigned to escort Plummer's widow, Julie, to Z rich, where a safety deposit box belonging to the Plummers has been discovered. Wolfe is assigned to stay at the Plummer residence, in Bethesda, Maryland to search for the secret project called GHOST, as well as look after the family's five children: Zoe, Seth, Lulu, Peter, and Baby Tyler.
The kids prove to be difficult to handle, even with the help of nanny Helga, who finally quits when one of Zoe and Seth's pranks intended for Wolfe goes wrong.
A few days later, the school's vice principal, Duane Murney, informs Wolfe that Seth has cut and bleached his hair, has a Nazi armband in his locker, and has skipped every wrestling practice for the past month. At home, a furious Seth tells Wolfe that he only joined the wrestling team because his father wanted him to. He sneaks out of the house, tricking the alarm system with a refrigerator magnet. Wolfe leaves Zoe in charge and follows him to the town theater, where he learns that Seth has secretly joined an amateur production of The Sound of Music. The director quits when he believes the show will be a failure. Wolfe volunteers to take his place, and juggles this task with taking care of the house, giving Zoe driving lessons, and teaching Lulu and the Firefly Scouts martial arts to defend themselves against the rival boy scout troop.
Seth quits the wrestling team, and Wolfe challenges Murney to a wrestling match in front of the entire school and easily wins despite Murney's show of bluster. The training Wolfe gives the Firefly Scouts becomes useful when they once again have a conflict with the thuggish scouts. Zoe and Wolfe share stories of their fathers, both of whom died in similar circumstances. They are interrupted by a phone call from Julie, who has figured out the password ("My Angel"), retrieved the item in a box (a special key), and is on her way home. The kids immediately begin to plan a 'Welcome Home' party. That evening, Wolfe discovers a secret vault underneath the garage, which requires a key to open. When Fawcett and Julie arrive home, Fawcett and Wolfe go to the garage, where Wolfe says he is rethinking his career. Two ninjas arrive armed and pull off their masks, revealing themselves as the Plummers' North Korean neighbors, the Chuns. Fawcett suddenly knocks out Wolfe, revealing himself to be a double agent. Mr. Chun restrains and guards the children while Fawcett and Mrs. Chun take Julie down to the vault. They manage to open the door, but a dangerous security system prevents them from going any farther.
The children manage to escape and awaken Wolfe, who sends the kids to get the police while he goes to the vault to help Julie. Mr. Chun follows them in his car; with Zoe at the wheel, the kids force him to crash. Wolfe figures out how to get past the security system, using a dance ("The Peter Panda Dance") Howard had used to make Peter go to sleep each night. Julie knocks out Mrs. Chun, and Wolfe's voice activates the final vault, knocking out Fawcett with the door. By then, the children have lured a large crowd of police to the house. Mr. Chun arrives and holds all of them at gunpoint. Wolfe notices school principal and love interest Claire Fletcher (Lauren Graham) right behind him, having followed the chase when she saw it pass by the school. Wolfe distracts Mr. Chun with the aide of Gary the duck, and Claire knocks him unconscious.
With the mission accomplished and Fawcett and the Chuns arrested, Wolfe and the Plummers say their goodbyes, and Wolfe and Claire share a kiss. At Seth's performance, it is revealed that Wolfe decided to retire from the Navy and join the school staff as the new wrestling coach. Murney also performs in the play, singing "Climb Ev'ry Mountain" off-key while dressed in a nun's habit.
Output: What secret project is Wolf instructed to find at the Plummer's residence in Maryland?