In a flashback sequence, Dr. Gordon (Cary Elwes) crawls from the bathroom to find help. Along the way, he reaches a hot pipe and uses it to cauterize the wound on his leg.
In the present, a crowd of people gather around a storefront window in an urban shopping area where they watch two men who are in a trap. The two are tied to a worktable, each with a buzz saw in front of them; their mutual lover is suspended above. As she is being lowered onto another buzz saw, each try to kill each other. After a brief fight in efforts to kill one another, both come to realize they will allow her to die because of all the trouble she has caused. They do nothing and watch her lower onto the buzzsaw, killing her.
The next trap sequence involves four people who are all connected to a car. The first person is glued to the drivers seat and must rip himself from the seat to reach a lever in front of him in order to save his friends. Jigsaw (Tobin Bell) explains that they are all racists and will die if the man in the drivers seat does not complete his task in 30 seconds. The car is on a jack so its hind wheels are above a woman's face. Another man is behind the car with three chains going through his lower jaw and two arms. Another man is seen in front of the car attached to the garage door. The man in the front seat tears himself away almost in time but fails. The wheels reach speeds up to 60 MPH(100km) and tear the woman's face off while also tearing off the man's jaw and arms. The car drives through the man attached to the garage door and smashes into a junk yard which flings the man in the drivers seat out of the windshield, tearing off his back and killing all four.
Several survivors of previous Jigsaw traps, including Dr. Gordon, attend a session held by self-help guru Bobby Dagen (Sean Patrick Flanery), who claims to have survived a Jigsaw trap and since then published a story about his encounter, becoming a celebrity. While Dagen is leaving the meeting, he is abducted by a masked person. He awakens in a cylindrical steel cage, and learns he must overcome certain challenges to save his wife, Joyce (Gina Holden) and others from death. Throughout his test, Joyce watches her husband via a TV screen, while she herself is wearing a collar, which is attached to the floor. As time passes, she is slowly dragged closer and closer to the ground.
The first person he must attempt to save is revealed to be his publicist, who is locked in a circular trap with four spears each pointing directly at her neck from a different direction. As Jigsaw reveals the key to be dangling by a string from her mouth all the way down her throat to her stomach, Dagen attempts to pull it out, but has difficulty as it is attached to a fishhook, and the room is wired with a decibel reader which will activate the spears if she screams. Eventually, the spears are propelled into her neck,and she dies. He next encounters his lawyer, who is strapped down onto a giant spinning wheel which will rotate her into a series of spikes (which will pierce her eyes and mouth), unless Bobby can use his shoulders to lift a large, heavy weighted device, in order to complete an electrical circuit which will stop the trap. However, the weighted device is also connected to a spike which pierces Bobby's side, and he is unable to hold it up. She dies from the spikes piercing her eyes. Afterwards, he encounters his close friend, who has been blindfolded and must rely on Bobby's directions to navigate himself over a series of narrow boards poised above an open section of floor. Should he fall, or not make it to the nearby hanging key in time, he will hang. He almost gets the key, but drops it, and is hung to death. We also learn that these three all knew Bobby was lying about being in a Jigsaw trap. He claimed he was in order to profit from his false story. Bobby is then forced to pull out two of his wisdom teeth in order to find a keycode to a locked door, which have been engraved on them. Finally, he ends up in the last room with his wife. He must attach two hooks to his chest and pull himself up towards the ceiling by the skin of his pectoral muscles, which is exactly how he had claimed to escape Jigsaw the first time in his book. He must connect a cable to free his wife, but he fails to do so because the weight of his body causes his skin to rip free of the hooks and he falls to the ground. His wife's trap activates, creating a Brazen bull. It begins to burn from the outside as Dagen tries to save her by climbing over the fence, but gets electrocuted and knocked unconscious and Joyce burns to death in the furnace.
Meanwhile, after escaping the reverse bear trap, Mark Hoffman (Costas Mandylor) stitches his wound and begins to track down Jill Tuck (Betsy Russell), who has given Hoffman away to the internal affairs in exchange for police protection and immunity. Hoffman sneaks into the station hiding in a body bag killing officers along the way. Hoffman finds Tuck and knocks her out, straps her in a chair, and puts the original reverse bear trap on herkilling her. As Hoffman exits and returns to his hideout, he finds out that he has been discovered, and destroys the hideout. He is soon attacked by three persons in pig masks, one of which reveals himself as Dr. Gordon.
It is then revealed that after Dr. Gordon escaped from the bathroom and cauterized his foot, he was nursed back to health by Jigsaw, who congratulated him on surviving. Jigsaw fits a prosthetic leg on him and allows him to help in his future traps, such as placing the key behind Michael's eye in Saw II, suggesting Lynn Denlon as a test subject in Saw III, and sewing Trevor's eyes shut in Saw IV. It is also revealed that it was Dr. Gordon who wrote the "I know who you are" letter to Hoffman in Saw V. In the tape that Tuck delivered to the hospital in Saw VI, Jigsaw asks Dr. Gordon to look over Jill and to make sure no harm comes to her. As instructed to do if she were to die, Dr. Gordon places Hoffman in the same bathroom as the first film, throws away the same hacksaw that he used to escape, Hoffman begins screaming at Gordon in a furious rage and before he shuts the door, Gordon looks at Hoffman and says "Game Over". He locks Hoffman in the bathroom, leaving him to die.
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