Sean Donovan grows up under the shadow of an abusive father and a mother who dies in a carjacking. After the tragedy, Terry Donovan moves the family to a quieter, nicer neighborhood. A decade passes, and Sean becomes an exceptional student who keeps everyone at a distance. He sees strife in everyday arguments and, craving control, trains in self-defense and starts carrying a weapon at night. When he defends himself during an attempted mugging, he ends up killing a man. An eyewitness account draws the attention of a rising NYPD homicide detective, Teresa Ames, who begins to take a closer look at Sean as he relentlessly searches the city’s police stations for anything that might point to his mother’s killer.
As Sean’s ties to violence deepen, he protects a young woman from an abusive pimp, engages in a brutal confrontation, and ends up killing him. The detective’s curiosity turns more personal once she gains access to his world, and she learns about his fixation on a toxin named Tricelaron, which he insists figures into a chemistry paper he is writing. A later odd detail—his fluent Chinese when he angrily confronts rude staff at a restaurant—adds another layer to the mystery surrounding his past.
On a crowded train, a volatile man taunts a Chinese family and other passengers. Sean steps in, speaking in Chinese to tell the boy to tell his family to leave, then secretly dons black face paint and brutally beats the aggressor with brass knuckles. The detective and her partner are aboard, but Sean escapes before anyone can identify him.
The detective’s pursuit of truth intensifies as she discovers the attacker spoke fluent Chinese and begins to suspect Sean. Her supervisor warns against pursuing the lead, but a retired superior eventually reveals crucial details: Sean could have named his mother’s killer from a photo book, but his father, Terry, coaxed him to change his story. The killer is identified as Larry Childs, a contract killer who was arrested months earlier, given a two-year sentence, and placed into witness protection via a plea deal.
Walking the street, Sean is overwhelmed by the harms he’s witnessed in other households. During a school party, a violent flashback of his mother’s murder surges through him, and he recalls hearing the killer address his father with an old boxing nickname. In a moment of fury, he savages a fellow student who taunts a female friend. The detective uncovers a photo at Sean’s home showing Terry with the killer, confirming that the two men knew each other long before the attack.
Convinced that Terry staged the assault to secure life insurance and pay off debts, Sean confronts his father. Terry denies killing his wife, but Sean’s conviction only grows stronger as he learns that his father sabotaged the original identification. He shoots and kills Terry, and when the detective finds him, Sean claims someone broke into their home and killed his father. She spots the murder weapon and destroys it.
Sometime later, Sean reaches out to Larry Childs with a disturbing request for the truth. He forgives the killer but asks him to reveal whether his father was involved in his mother’s death. He provides a self-addressed envelope with two stamps—a red stamp for “father innocent” and a black stamp for “father guilty.” Larry licks the stamp and, after passing it to a guard, collapses, unable to breathe. Sean receives the letter and stares at the red stamp, knowing the truth may forever remain hidden.
