A corrupt Drug Enforcement Administration agent and his thugs murder 12-year-old Mathilda's family in a drug deal gone awry. Orphaned by the massacre, Mathilda is forced to take shelter in the apartment of a neighbor, Leon, whom she knows only slightly. He's a loner and first generation immigrant, who also happens to be a professional hitman. He's never had reason to care about anybody and she has no one else to turn to. Together, they form a makeshift father and daughter bond that will forever change both their lives.