The film dramatizes the 2013 Boston Marathon bombing and the subsequent four-day investigation and city-wide manhunt. The narrative follows a composite character, Boston Police Sergeant Tommy Saunders, who is present at the finish line when the bombs detonate. The plot chronicles the immediate chaos, the emergency response, and the launch of a massive investigation led by the FBI to identify the perpetrators. The film culminates in the identification, pursuit, and eventual neutralization of the two terrorists, Tamerlan and Dzhokhar Tsarnaev.
The core of the film focuses on the procedural steps taken by law enforcement. After the initial attack, FBI Special Agent Richard DesLauriers takes charge, establishing a command center to analyze vast amounts of video surveillance and photographic evidence from the public. This meticulous process leads to the identification of two suspects. The narrative's turning point occurs after the FBI releases the suspects' images, prompting them to murder MIT Police Officer Sean Collier and carjack a civilian, Dun Meng. Meng's escape provides critical intelligence, leading authorities to the suspects' location in Watertown, Massachusetts, and instigating a violent firefight.
The resolution of the events begins with the Watertown shootout, during which the elder brother, Tamerlan, is killed, and a police officer is critically wounded. The younger brother, Dzhokhar, escapes, triggering a lockdown of the greater Boston area. He is ultimately discovered hiding in a boat in a residential backyard, located via thermal imaging from a police helicopter. Following a brief standoff, the wounded Dzhokhar is taken into custody. The film concludes by transitioning from the dramatization to documentary footage of the real-life survivors and heroes, emphasizing the resilience of the community through the "Boston Strong" movement.
