A four-year-old girl just disappears from her home on a Boston block. The missing child's aunt, not receiving sufficient efforts from the police representatives, in her opinion, hires two private detectives Patrick (played by the director's younger brother Casey Affleck) and Angie (actress Michelle Monaghan). Although both shallowly try to abandon the new investigation, arguing that missing children cases are not their specialty, the family of the missing girl wants this particular couple. Firstly, they are not the police, secondly, the detectives themselves come from the neighborhood, so they know everyone around them.
Little by little, the details of the case begin to paint a coherent picture. The detectives deal with drug dealers, gang members, pedophiles and other criminals and step by step get closer to the kidnapped little girl. However, none of them realizes that the real moral dilemma and the greatest difficulties await them when it seems that the case has already been solved.