WARNING: This synopsis is written with the events of the films arranged in chronological order, rather than in the order of which film they happened in. Since the films jump back and forth chronologically, especially in the latter installments, you cannot avoid spoilers by stopping or skipping around when you see events with which you are not familiar. Reading this page will spoil the major details and reveals of the entire franchise. Read on or go back—make your choice.
John Kramer is an successful civil engineer who coasts through life without worry—until the night his wife Jill, a doctor working in a rehab clinic, is attacked by one of her patients. The attack causes the stillbirth of the son Jill and John were expecting; the couple divorces afterward. Soon after that loss, John learns that he has a frontal brain tumor which doctors cannot operate on. And just so life could twist the knife further, John's insurance company refuses to fund an experimental treatment that could at least alleviate his suffering, if not outright cure him. The death sentence handed to John fills him with bitterness at all the healthy people around him who take their lives and situations for granted.
To end his suffering, John attempts suicide by driving his car off a bridge. He survives the attempt against all odds, and the experience grants him a twisted form of clarity about his future: He needs to help "rehabilitate" people into appreciating their lives. But how would he do this? Why, the same way he gained appreciation for his own life—he would subject them to nightmarish death traps, or "games", where anyone who survives would cherish the life ahead of them. Those who failed would, of course, have no life to appreciate.
John's crusade begins with the kidnapping and killing of the patient who attacked Jill, but it certainly does not end there. Bodies pile up as Kramer tries his best to teach people the value of their own lives. The police soon catch on, as does the press, which names him the "Jigsaw Killer", or "Jigsaw", due to the jigsaw-shaped piece of flesh cut out from his "patients"—a symbol of the "missing piece" of their life that prevented them from being "rehabilitated". One of the few victims to "win" his "game" is Dr. Lawrence Gordon, the doctor who diagnosed Kramer with the brain tumor; Gordon escapes his trap, but he has to cut off his own foot to do so.
A young drug addict named Amanda—who helped Jill's attacker and unwittingly set into motion the events that led to the Jigsaw killings—also managed to win her "game" and escape with her life. Her survival leads her to seek out Jigsaw and become his apprentice. Jigsaw accepts her as his accomplice, and the pair work together to round up new victims. But she would not be the only person whose help Jigsaw enlisted. Detective Mark Hoffman, a police officer who wanted to avenge his sister's murder, kidnaps his sister's killer, places him in an inescapable death trap meant to resemble one of Jigsaw's, and watches the perp die. Jigsaw discovers Hoffman's handiwork and blackmails the detective into becoming another apprentice.
Amanda and Hoffman both create inescapable traps based on Jigsaw's handiwork—Amanda does it because she believes Jigsaw's methods are too lenient, while Hoffman does it to cover his tracks and pin the crimes on Jigsaw. The two apprentices never see eye-to-eye, so Hoffman blackmails Amanda into killing one of Jigsaw's last "patients"—Amanda was still using drugs even after surviving her "game", and Hoffman knew that Amanda had been at the clinic when Jill was attacked. The shooting costs Amanda her life, and Jigsaw himself dies soon afterward after his throat is cut by the "patient's" husband in an act of vengeance.
FBI agent Peter Strahm manages to discover Hoffman's role as a Jigsaw apprentice, but Hoffman kills Strahm in a deathtrap and frames him as Jigsaw's second accomplice. Hoffman's run of "Jigsaw" victims leads to further investigation by the police, who unearth tapes of Hoffman's vocal imitations of Jigsaw. The police de-scramble the tapes and hear Hoffman's voice loud and clear, but Hoffman kills everyone in the room and burns the evidence to protect his secret. He returns to oversee Jigsaw's final game—which involves the insurance agent who denied Kramer's coverage application—but soon learns about Jigsaw's actual final game: Jill Tuck, Jigsaw's ex-wife, puts Hoffman in a trap without any instructions for escaping and leaves him to die. Hoffman survives the game due to some quick thinking, after which Jill narrowly escapes Hoffman's clutches and reports him to the police in exchange for protection.
Hoffman uses video messages to demand the police turn Jill over to him; if they don't, the Jigsaw killings will continue. The police refuse, so the current "game" keeps going (and ends as poorly as most of the rest), while the officers hunting Hoffman soon meet their own demise. Hoffman sneaks into the police station by hiding in a body bag, then methodically kills the officers still in the station and puts Jill in the original Reverse Bear Trap without any means of escape. She dies when the trap tears her face apart.
Hoffman destroys his hideout and any remaining evidence of his crimes. He believes he is victorious...but as he flees, he is captured by the one person no one would ever suspect: Dr. Lawrence Gordon, who survived his "game" by sawing off his foot and cauterizing the wound as he crawled away. Jigsaw saved Gordon from dying, fit him with a prosthetic foot, and turned him into Jigsaw's real apprentice. Gordon became privy to all of Jigsaw's schemes, unlike both Hoffman and Amanda; he even helped set up traps and pick some of Jigsaw's later victims. Jigsaw also made sure to give Gordon one last task, just as he did with Jill: If Hoffman ever tried to go after Jill, Gordon was to kill Hoffman in revenge.
The ending of Saw 3D echoes the ending of the first film: Gordon chains Hoffman to a pipe in the same bathroom where Gordon played his "game". Because Hoffman crossed the line by killing Jill, the "good" doctor removes anything that could help Hoffman escape, leaving him to die.