A hardened CIA operative finds himself at the mercy of a precocious 9-year-old girl, having been sent undercover to surveil her family.
JJ is a new CIA agent and a former Army Ranger. But because of his lack of tact, he fails to carry out his first significant mission, which was to stop the Russian mafia and a Middle Eastern terrorist named Hassan from engaging in an illicit weapons-grade plutonium trade in Pripyat.
Even so, his boss David Kim has JJ and tech operator Bobbi, who idolizes JJ, watch over the in-laws of Victor Marquez, a French illegal arms dealer who has construction plans for a miniature nuclear bomb that he plans to sell to Hassan.
David, Victor's brother, stole these plans from Victor and concealed them before Victor killed him. After David passed away, his American wife Kate and their 9-year-old daughter Sophie returned to Wicker Park, Chicago, from France, and Kim believes they might be with them.
After moving into the building where Kate and Sophie reside, JJ and Bobbi install their surveillance system. Sophie quickly locates one of their covert cameras, reverses its signal, and discovers the operation post. As she attempts to blend in with American children and make some new friends at Oaktree Charter School, she confronts JJ and Bobbi and uses blackmail to get JJ to keep her company.
The two gradually start to get along despite JJ's social awkwardness, and JJ also gets to know Kate's neighbors Carlos and Todd. Sophie brings him and her mother closer together by having JJ teach her the fundamentals of the espionage trade.
Kim, however, removes JJ and Bobbi from the mission after learning of his personal involvement with his targets. Kate rejects JJ out of disgust after he tells her about his assignment. Simultaneously, Victor uncovers and thwarts the CIA's surveillance and forces his attorney Koll to divulge possibly secret locations for David's plans.
Victor travels to Chicago after staging his own death, confronts Kate, JJ, and Sophie, and takes the plans back. Todd and Carlos, who are also pursuing the plans, interrupt and reveal themselves as independent arms dealers. As a result of Bobbi's awkward attempt to assist, Victor escapes with the plans and takes Sophie hostage.
After pursuing Victor to an airfield in Naperville with Kate, JJ grounds Victor's escape plane and engages him in a fistfight. The plane hangs on some wire fencing at the edge of a cliff after Sophie unintentionally starts it moving during her escape attempt. Sophie has concealed the true plans, but Victor makes her give them up. JJ pushes the plane off the cliff, killing Victor before he can shoot them, and Kate clubs him onto the fence.
JJ is permanently assigned to Chicago after being rehired by Kim due to his achievements, and he lives with Kate and Sophie there.
