The film kicks off with Michael (played by Noam Jenkins), a police informant, who unwittingly becomes trapped in a perilous game orchestrated by the notorious Jigsaw Killer (voiced by Tobin Bell). In a chilling videotape, Michael learns that a spiky helmet resembling a Venus flytrap is locked around his neck. Unless he can retrieve the key embedded behind his right eye, the device will close in, leading to his demise. In a moment of despair, Michael finds a scalpel but struggles to inflict injury on himself. As time ticks away, the device shuts, resulting in his gruesome death.
Meanwhile, tensions arise between Detective Eric Matthews (Donnie Wahlberg) and his rebellious teenage son Daniel (portrayed by Erik Knudsen). Matthews is summoned to investigate another murder executed by Jigsaw, where his name ominously appears on a wall. Observing a padlock on a victim's neck marked with the Wilson Steel logo, Matthews assembles a SWAT team and heads to an abandoned factory that serves as Jigsaw’s new lair. Inside, a series of monitors reveal several captives trapped in a mysterious house, including his son Daniel. With a timer ominously ticking down, Jigsaw, weakened by terminal brain cancer, informs Matthews that he will reunite with his son in a safe setting if he engages in lengthy conversation with him.
As the captives, including Amanda Young (Shawnee Smith) who was the only survivor from the first Saw film, begin to piece together their shared predicament, tension escalates. Seven individuals find themselves in a race against time with a toxic nerve gas slowly infiltrating the house, threatening their lives. Jigsaw's tape reveals that the door to their escape will only open in three hours, yet death looms ever closer. Among the group, the characters must navigate through treacherous traps and each other's hidden pasts, while struggling to find antidotes hidden within a locked safe.
As a series of dangerous events unfold, including brutal confrontations and shocking betrayals, the captives soon discover the horrifying truth: they are all individuals who were wronged by Matthews in the past. While Matthews frantically seeks clues to rescue his son, the complexities of trust and survival ignite conflict among the captives. As lives hang in the balance, the story plunges deeper into the psychological torment orchestrated by Jigsaw, showcasing his twisted philosophy of justice.
In a shocking climax, Matthews finds himself chained and confronted by Amanda, who has now become Jigsaw's apprentice. The transformation of Amanda from a victim to a vengeful accomplice sets a chilling tone, as she locks Matthews in a deadly trap, revealing that he is her first target. As she utters, > "Game over!" the grim realization of Jigsaw's master plan lands heavily upon the audience, culminating in a dark twist that reflects the series' ongoing themes of revenge and redemption. Outside, Jigsaw ensures his sadistic satisfaction as his meticulously crafted game reaches its horrifying conclusion.
