Plot[edit]
Adam Stanheight, a photographer, awakens in a full bathtub in a large dilapidated bathroom. He gets out and finds himself chained at the ankle to a pipe. Lawrence Gordon, an oncologist, is chained to a pipe across the room and between them lies a corpse, holding a revolver and a microcassette recorder. Adam manages to retrieve the recorder and they learn from tapes in their pockets what they must do: Adam must escape the bathroom before six o' clock, and Lawrence must kill Adam before six o'clock, or his wife and daughter will die and he will be left to die as well. Using a clue from the tape, Adam finds a bag in the toilet tank containing two hacksaws, though neither is able to cut through their chains. Adam's saw breaks and he throws it at a mirror in frustration. Lawrence realizes the saws are meant to be used on their feet and identifies their captor as the Jigsaw Killer, whom Lawrence knows of because he was once a suspect.
Flashbacks show that while Lawrence was talking with some medical students and an orderly named Zep Hindle about the terminal brain cancer of a patient named John, he was approached by Detectives David Tapp and Steven Sing about his penlight being found at the scene of a Jigsaw "game". His alibi clears him, but he agrees to view the testimony of Amanda Young, a heroin addict and the only known survivor of Jigsaw's games, who believes that her experience has made her a better person.
Meanwhile, Alison and Diana, Lawrence's wife and daughter, are being held captive in their home by Zep, who is watching Adam and Lawrence through a camera behind the bathroom's mirror. The house is simultaneously being watched by Tapp, who has been discharged from the force. Flashbacks show that Tapp became obsessed with the Jigsaw case after hearing Amanda's testimony, and found Jigsaw's warehouse using the videotape from her game. He and Sing entered Jigsaws warehouse, where they saved a man from a drill trap, but Jigsaw escaped after slashing Tapp's throat, and Sing was killed by a shotgun trap while pursuing him. After being discharged, Tapp began stalking Lawrence still convinced that he is Jigsaw.
In the bathroom, Lawrence finds a box containing a lighter, two cigarettes, and a one-way cellphone. Lawrence then recalls his abduction: he was trying to use his phone after being trapped in a parking garage, and was suddenly attacked by a pig-masked figure. The two try to stage Adam's death using a cigarette supposedly tainted by the corpse's poisoned blood, but the plan fails when Adam is shocked through his ankle chain. Adam then recalls his own abduction: he woke up in his photo development room to find the power was out and, after finding a puppet, was attacked by a pig-masked figure as well. Lawrence receives a call from Alison and is told not to trust Adam. Adam admits he was paid to take photos of Lawrence and reveals his knowledge of Lawrence's affair with one of his medical students. He then shows him several photos from the bag that contained the hacksaws. Lawrence tells Adam to describe the man who was paying him, and realizes it was Tapp. Adam later finds a photo he didn't take, of a man staring out a window of Lawrence's house. Lawrence identifies him as Zep, but the clock strikes six as he realizes this.
Alison, manages to free herself, and after Zep calls Lawrence she fights him for the gun. The struggle gets Tapp's attention, and he saves Alison and Diana. He then follows Zep to the sewers, where he is shot after a brief struggle. Lawrence, who is only aware of gunshots and screaming, is shocked and loses reach of the phone. In desperation, he saws off his foot and shoots Adam with the corpse's revolver. Zep enters the bathroom intent on killing Lawrence, but is knocked to the ground and beaten to death with the toilet tank cover by Adam, who only suffered a flesh wound. After Lawrence crawls away to get help, Adam searches Zep's body for a key and finds another microcassette recorder, which reveals that Zep was another victim, who was following rules in order to obtain an antidote for a slow-acting poison in his body. As the tape ends, the "corpse" rises and reveals himself as John, the real Jigsaw Killer. He says that the key is in the bathtub, which went down the drain when Adam first awoke. Adam tries to shoot John with Zep's pistol but is shocked by John's remote control and loses reach of the gun. John then turns off the light and seals the bathroom door, leaving Adam to die.