Private investigators Patrick Kenzie and Angela Gennaro are hired to find a missing four-year-old girl, Amanda McCready, from a working-class neighborhood in Boston. Amidst police efforts led by Captain Jack Doyle, who is deeply affected by a personal tragedy involving his own child, the investigation uncovers the neighborhood's complex web of criminal activities, drug dealings, and pedophile rings. The local community is distrustful of law enforcement due to a history of corruption and cover-ups, and the pair must navigate this difficult terrain to make progress in their search. As they delve deeper, their relationship is tested by the moral complexities of the case and the grim realities they uncover.

Their inquiry leads them to a series of convoluted leads and morally ambiguous situations. They interact with various shady characters, including drug lords, informants, and corrupt cops, who all seem to have their own agendas and opaque connections to the missing child's situation. The relationship between Patrick and Angela becomes increasingly strained as they confront their own ethical boundaries and the perilous nature of the world they've become involved with. They find that every twist in the investigation forces them to question their motives and the very nature of right and wrong. The search for Amanda exposes the fragilities of the justice system and the many shades of human guilt and innocence in times of crisis.