During a lively Fourth of July parade, Detective Marv Boswick finds himself in a perilous chase after a thief who slips into a sewer drainage pipe. However, his pursuit takes a dark turn when he is ambushed by a masked figure clad in a pig mask. Upon awakening, he discovers himself suspended by his tongue in the midst of a bustling subway tunnel, faced with a terrifying choice through a recorded message: tear out his tongue to escape or remain until the next train arrives, sealing his fate. Unfortunately, Boswick runs out of time and is tragically killed by the oncoming train.
The following day, Captain Angie Garza assigns the task of investigating Boswick's demise to Detective Ezekiel "Zeke" Banks and his enthusiastic rookie partner, William Schenk. As they delve deeper into the case, Banks realizes that the circumstances surrounding Boswick's death bear a striking resemblance to the notorious Jigsaw Killer, who is now deceased.
In a parallel thread, a homicide detective named Fitch, who had previously ignored a distress call from Banks leading to a near-fatal incident, is taken captive and thrust into a horrific trap. He faces a horrifying choice: rip his fingers off to avoid being electrocuted in a rapidly filling basin of water. Sadly, Fitch also fails to survive the ordeal.
As the investigation unfolds, suspicions arise among some officers regarding Banks' possible involvement, largely due to his complicated history with Fitch. The plot thickens when a mysterious box arrives at the precinct, containing a sinister pig puppet and a piece of skin adorned with Schenk's tattoo. The box includes a small vial, directing the police to a former butcher shop, a nostalgic haunt from Banks' childhood with his father, Marcus Banks. Upon their arrival, the team discovers a tape recorder alongside a skinned corpse, which is identified as Schenk.
Determined to track down the killer, Marcus ventures into a warehouse, where he too falls victim to abduction. Shortly thereafter, Garza faces her own fate, becoming trapped in the precinct's cold storage. Here, she must sever her own spinal cord using a blade to halt hot wax from dripping onto her face. Though she manages to free herself from the immediate threat, the injuries she incurs prove fatal, leaving Banks devastated upon discovering her lifeless body.
In a desperate turn of events, Banks himself is captured and awakens restrained to a pipe in the warehouse, where he finds only a hacksaw within reach. He contemplates a drastic measure—sawing off his own arm—but instead uses a bobby pin to unlock his cuffs. As he navigates the warehouse, he encounters Pete, his former partner who was dismissed after Banks exposed a murder he committed. Together in the room, Banks faces a daunting mechanism rigged to fire glass shards at him. A tape recording offers him a chilling ultimatum: free Pete or allow him to perish. Despite his best efforts to save Pete, he succumbs to blood loss.
In another twist, Banks discovers that Schenk is alive, having faked his own death using the corpse of the thief who lured Boswick into the subway tunnels. Schenk reveals himself as Emerson, the aggrieved son of the man Pete murdered, shot for agreeing to testify against a corrupt officer. He further explains how Marcus had prioritized the elimination of crime over protecting law enforcement integrity.
Emerson views Banks as a potential ally, presenting him with one final, harrowing test. He reveals Marcus restrained above, slowly losing blood. After calling 9-1-1 under false pretenses, he hands Banks a revolver containing a single bullet, forcing him to choose: shoot the target to save his father while allowing Emerson to escape, or eliminate Emerson, sealing his father's doom. Ultimately, Banks opts to shoot the target, causing Marcus' restraints to loosen. However, the arrival of the SWAT team triggers a terrible chain reaction, resulting in Marcus being pulled upward and inadvertently shot due to a concealed weapon. Overwhelmed with anguish, Banks watches helplessly as Emerson escapes into the night.
