The film begins with Detective Eric Matthews (Donnie Wahlberg), chained by the ankle in the same dilapidated bathroom he was imprisoned in at the end of Saw 2. He uses his boot to get his gun and a flashlight - his only light source - finding out his gun's clip is empty. He spots the corpses of Xavier (Franky G), Adam (Leigh Whannell), and Zep, as well as Dr. Gordon's severed foot. Eric attempts to saw through the ankle chain with a small saw similar to what Dr. Gordon used, but to no avail. About to cut his own foot off, he decides not to go through with it, possibly realizing he could bleed to death. Instead, he grabs the nearby toilet lid and begins begins to brutally pound upon his own chained foot, crushing it, then forcably breaks his ankle to allow his foot to slip out of the chain.
Than Twards The End Of The Middle:
In the warehouse, Lynn begins to operate on John. After cutting away the skin on his head, she drills and saws into his skull, removing a portion of it relieve pressure in his brain from the hernia. Jigsaw's heart rate beings to decrease, and he hallucinates, having flashbacks of walking in a sunny park with a blonde curly-haired woman, while Amanda screams hysterically. Jigsaw soon stabilizes and Amanda watches as he holds Lynn's arm and then says he loves her, still momentarily stuck in his hallucination. Jealous, Amanda leaves, a flashback showing her agreeing to give up every cell in her body for John. The flashback reveals that she kidnapped Adam prior to the events of Saw I. In the present time, Amanda, stricken with grief, cuts herself on the thigh, a new addition to numerous scars assumed to be from the same practice before (it is speculated that each of these scars represents a victim from her own vicious traps). Lynn, in the other room, puts on her wedding ring again and cleans herself up. Amanda enters and hugs John, only to be scolded by Lynn for touching him. Amanda confronts Lynn, about to brandish a gun, but John interferes and tells Amanda to leave. Once she leaves, he apologizes for Amanda's behavior, noting that her emotional nature is her weakness
Twards The Turning Point To The Middle
In a flashback sequence, Amanda is shown returning to the bathroom where Adam is locked with the dead body of Zep. She sets her flashlight down and goes up to him, slowly waking him up and telling him that she's going to help him. She then wraps a plastic bag around his face while telling him to breathe, then begins to breakdown and cry in her insanity. Adam eventually dies.
The Conclusion Of The Middle
Amanda shows up to see Jigsaw holding Lynn's hand, and Jigsaw tells her to leave. She does, in a jealous rage, returning quickly with her gun to reveal that Jeff passed the third test. Jigsaw tells Amanda to release Lynn, but she refuses, cocking her gun and pointing it at Lynn. He attempts to calm her, claiming she would not be following the rules, but Amanda refuses to listen. Jigsaw begs her to listen and says Lynn is far more important than she knows. Amanda feels betrayed by her mentor and lashes out at him, as he condemns her for her past crimes, where she killed people rather than giving them a chance to leave alive. Jigsaw forgave her for all of this, and cleaned up her mistakes. Amanda eventually admits she is a murderer, and flashbacks to her confrontation with Eric Matthews.
In the flashback, Eric has opened the door to his prison and is hobbling down the hallways. Amanda is still around, emotional and distraught, but quickly realizes Eric is out of the room. They find each other, and Eric brutally attacks her, slamming her face into the wall and asking where his son is, calling her a 'f*****-up junkie b****' in the process. Amanda refuses to tell him anything, kicking out his broken ankle and stumbling away. Eric recoils in pain and screams down the halls, calling her a 'b****,' telling her that she is nothing, and that she is no Jigsaw. While he screams and taunts her, she stands up and gets a stone cold expression on her face (while Eric's fate is not shown, it is implied that she killed him, which the producers of the film have confirmed).
The End:
Back at the warehouse, Jeff discovers a gun and inserts the magazine he found previously, before continuing down the corridors toward the exit. Jigsaw and Amanda continue to argue as Jeff arrives in the immediate area. Lynn goes to embrace him, and a noticably distraught Amanda shoots her in the back. Lynn collapses in Jeff's arms. Jeff immediately raises his gun and shoots Amanda in the neck. Amanda recoils, wide-eyed with surprise, appearing to have not known Jeff received a gun. Jigsaw stares at her and reveals his true plan all along: Amanda was the one being tested. Lynn and Jeff were actually married (Lynn had been cheating on Jeff with Chris earlier in the movie), and he was the one who set up the boxes in the corridors for Jeff's tests. In his desperation to make her his true apprentice, after all the injustices she had committed with her murders, he gave her one last chance. He also claims that all the "games" that Amanda has set up are "unwinnable", referring to Troy's welded room and Kerry's torso device. By disobeying the rules and shooting Lynn, she had failed. Amanda can only listen to him with her wound bleeding, before collapsing and dying. Jigsaw then utters the words "Game over."
A few feet away, Jeff has set Lynn against the wall. He initally points the gun at Jigsaw, whom tells Jeff he can't kill him. Jeff, possibly knowing there's no bullets left, clicks the trigger once and goes back to his wife, who is starting to speak again. Jigsaw tells him she is dying, and to stand and face him. If he co-operates, he can call an ambulance to arrive in 4 minutes. Jigsaw proposes one final test. On a nearby table, there are various tools about that Jeff can use to exact his revenge on Jigsaw, or he can forgive him for the pain he's caused Jeff and Lynn. "Live or Die," Jigsaw says, "make our choice." Jeff claims he forgives him, but then brandishes a circular saw. Jigsaw smiles, while Lynn desperately tries to tell Jeff to stop, but she can hardly speak. Jeff slices Jigsaw's throat open, once again proclaiming "I forgive you."
Jigsaw begins to flatline and reveals a tape recorder in his right hand, playing it. The tape reveals that Jigsaw himself was the final test. For as he said earlier, Jigsaw was the man responsible for the loss of his child: His daughter. Only he knows where Jeff's daughter is, locked behind a door the camera views momentarily, and that she is running out of air. By killing him, Jeff has failed the final test, and learned nothing in his ordeal. For living a life consumed by vengeance and hatred, he must now be punished. Lynn's collar light flashes red, the doors of the warehouse, room and latch shut (seemingly also monitored by Jigsaw's heart rate). Jigsaw flatlines, causing the collar to go off, blowing Lynn's face away and killing her instantly. We are treated to a montage of imagery compiled from all three films as Jigsaw finally dies, and Jeff's screams of terror echo through what has now become his tomb.
