It is New Year's Eve in 2022, and the city of Baltimore is complete with people partying in their apartments or just going about their business. Amidst this chaos, as soon as a round of fireworks goes out, 17 people are shot dead with bullets flying out of nowhere at multiple locations. On the other side of the town, Eleanor Falco (Shailene Woodley), a police officer, is trying to settle a meager squabble at a diner involving an alcoholic homeless woman who refuses to leave the diner when she is paged to reach one of the sites of the shooting.Eleanor arrives at the site, and the police ascertain that all the bullets have been fired from a certain 17th floor apartment in the neighborhood. It is at the precise moment of this discovery the apartment blows up, sending a shock wave of panic among the other residents in the building. All the police personnel immediately rush to the site of destruction. Eleanor, along with one of her colleagues, stands outside the building recording videos of the fleeing residents. There was a possibility that the culprit was in the crowd.Soon, the police and the FBI reach the site and find no trace of the perpetrator. Eleanor, who had by this time climbed the stairs to the 17th floor without a gas mask while resting against one of the walls of the apartment due to ill health, manages to hint at investigating the toilet for any possible evidence of the shooter.Back at the police station, the chief FBI investigator, Geoffrey Lammark (Ben Mendelsohn), arrives and briefs the department about the task they have at hand - finding out the mass shooter - and explains the things they need to keep in mind while carrying on investigations. He particularly fancies Eleanor, who is prompt to tell him that the shooter is unlikely to strike again and why.We get an insight into the lonely life of Eleanor as she returns home that night. However, very early the next morning, she is summoned by Lammark. The latter insists that she assist him in this case because her thought process would be insightful, and she could also serve as the link between the Baltimore Police Department and the FBI in this investigation. Here, they meet Jack Mackenzie (Jovan Adepo), another FBI agent who would be following them closely in finding the shooter. What follows is a lot of brainstorming among the three as they try to understand the possible motive of the attack or the reason why it took place. We also understand that Lammark is under huge duress from the FBI authorities to successfully find the shooter.While Eleanor, Mammark and Mackenzie are still trying to figure out who the killer is, the investigators have narrowed it down to a teenage boy - who has confined himself to his room and watches ISIS videos - as their primary suspect. They proceed to zero down on him, despite Lammark's orders. Unfortunately, the boy jumps out of his bedroom window and dies in the process.As the authorities press upon Lammark to find the shooter, he invites Eleanor home and introduces her to his husband... revealing himself to be a closeted homosexual. Lammark also confronts Eleanor about her FBI rejection, citing psychiatric issues such as depression as the reason. She confesses that she took up a job in the police force to save her from her own self-destructive tendencies.A few days later, another horrific incident takes place. In a shopping mall, a man is seen stealing the clothes of a guy from the male changing room and washing it clean in the sink area of the toilet. Another man spots him in the act and informs the mall security guards about this unaccepted behavior, who try to trace the stranger down. When they finally find him, he is stealing food at the food court. As the guards tried to ask him to leave, the man pulls out a gun and shoots the people around him dead. He escapes from the rest of the police, who are after him, by blowing them up with grenades planted in a nearby dustbin. Lammark and Eleanor reach the place shortly afterward and are horrified by the nonchalance of the man.The news spreads like wildfire. The FBI takes down a group of local NRA members who support gun violence in another attempt at finding the perpetrator. In the course of the investigation, Lammark and Eleanor come to believe that the shooter has access to old guns and military equipment, and the lab stool result shows that the man was on a plant-based diet in the days following up to New Year's Eve. However, the authorities at this point have lost confidence in Lammark and his team after the second attempt at crackdown and both Lammark and Eleanore are removed from investigating the case any further. Subsequently, a realization strikes Eleanor, which finally leads her to the culprit. A man named Dean Possey (Ralph Ineson).Throughout the whole movie, the detectives at work come to identify the primary traits of this man - a white guy, not a meat eater, and someone with access to old military weapons. Luckily, one of the men who painted the apartment that originally blew up provides a facial sketch of Possey and directs them to search at a meat processing factory around where he was previously employed.Eleanor and Lammark find out about Dean from the older employees at a slaughterhouse and learn that Dean is believed to have killed one of his superiors, who was also a bully to him. This led to his imprisonment for two years before he was released on parole in December 1999. Possey's father, Sergeant Arthur Possey, was the shooting instructor of the 75th Rangers, and Dean's parole had been supported by letters