The film starts with Seth in the pendulum trap. The trap is later revealed to be unwinnable, but Seth is made to believe that the aim of the trap is for him to push buttons inside of two devices which would crush both of his hands before a bladed pendulum (intended to slice him in half) descends upon him. Meanwhile, Agent Strahm shoots Jeff and enters the room where Jigsaw died. After investigating and finding Jigsaw's corpse, the door is locked on Strahm. Strahm manages to exit through a secret door, and finds a recorder. The recording warns him he can find salvation or die in the room, and urges him to make the right choice. He disregards it, then is attacked by a figure in a pig mask. He wakes to find himself in one of Jigsaw's traps. His head is in a sealed box, which quickly starts to fill with water. Before he runs out of air, he performs a tracheotomy with the tube of a ballpoint pen in order to breathe. The police make it to the Gideon warehouse, and Hoffman emerges carrying Corbett, claiming that he saved her. Strahm is carried out on a stretcher, still alive, but badly injured. The next day the police hold a service for all the people who have died chasing Jigsaw. The Chief of Police announces that the Jigsaw murders are over. Jill is given a videotape and box from John's lawyer. The contents of the box, says John, are of grave importance to her. After looking in the box, Jill leaves without telling John's lawyer what's inside. Strahm is shown mourning next to a empty hospital bed, because Perez died in the night. Hoffman walks into the room. Strahm starts to act strange and says that Perez's final word was "Hoffman." Hoffman worriedly says he has no idea what Strahm is talking about. He heads back to his office and finds a note for him saying "I know who you are." Hoffman gets worried that the fact that he may be in danger. Meanwhile, five people wake up in a sewer, in a neck tie trap. This trap involves pulling against a cable to get a key at the end of the room to release themselves. The consequence for not completing the trap is to be beheaded. Mallack gets anxious and runs ahead, starting the timer. In the end, the whole group, except for Ashley, get their keys. Ashley is eventually beheaded by the blade once the cable is pulled tight. The group walk through a door to another room. Strahm, contemplating what his deceased partner said, starts to go mad and heads over to FBI headquarters to find files on Hoffman. He finds a file saying that Hoffman's sister was murdered, and her killer (Seth) was killed in his trap, which was revealed to have taken place before the events of the first film. Strahm comes to the conclusion that Hoffman killed Seth, but staged it as a Jigsaw trap. A flashback depicting Hoffman looking at the pendulum trap ensues, as he was the person watching at the start of the film. A couple of weeks after Seth's death, Hoffman is kidnapped by Jigsaw. Jigsaw blackmails Hoffman into working for him, which Hoffman reluctantly agrees to. Hoffman is then shown, through flashbacks, setting up the house trap, talking to Jigsaw before the events of "Saw IV", and kidnapping Paul. By the end of these events, Hoffman is a willing apprentice to Jigsaw. Back in the sewers, Charles, Mallick, Luba, and Brit make it to the next trap. In this trap, the group has to smash jars and find keys to enter bomb shelters before a bomb goes off in the sewer. Charles smashes Mallick's jar in an attempt to steal his key, but fails. Brit and Luba pick up keys. Mallick attempts to pick up a key but Charles steps in his hand and takes it. Just as Charles is about to enter his shelter, Luba hits him with a pole and gives the key back to Mallick. The trio enter the shelter and leave Charles to die by the explosion. Luba, Mallick, and Brit make it to their next test. In this test, they have to find a way for a cord of electricity to make it into a bath of water to complete a circuit opening the door to the next test, but the cord is not long enough to reach the bath, so they think they need to use a person's body. Luba tries to kill Mallick to use his body, but Brit stabs her in the neck, saying she never trusted her. Mallick and Brit use Luba's body for the electricity to reach the bath, and the door opens to their final test. Meanwhile, Hoffman plants Strahm's cell phone at the house where Brit and Mallick's game is being held, in hopes to frame him. Strahm is now sure that Hoffman is Jigsaw's apprentice. Meanwhile, Brit and Mallick make it to their final test. In this test they have to stick their hands into saws and bleed into a beaker. When the beaker fills with their blood, they will be free to go. Before they start the test they realize that there are five saws, they then realize that everyone could have made it through every test alive, if hurt. Only one key was needed to unlock each neck restraint in the first trap, the bomb shelters had room for two in the second trap, and each person could have sustained a mild electric shock to complete the circuit in the third trap. It is also revealed that they were all connected by an act of arson that happened some time ago which resulted in the death's of 8 people. In the final test, each could have given just just two pints of blood each and easily lived. With no other options, Brit and Mallick begin sawing their arms in an attempt to fill the beaker meant for five with 10 pints of their blood. Just as Brit and Mallick fill the beaker with blood, finishing the final test, a FBI agent named Erickson (Strahm's superior whom Hoffman fooled into trailing Strahm's cell phone signal) makes to the scene. Both pass out from blood loss as Erickson calls for backup. It appears as though Brit and Mallick survived. FBI agent Erickson, having found the Jigsaw files Strahm took and his cell phone, issues an APB on Strahm, assuming him to be the other Jigsaw accomplice. Strahm follows Hoffman to the location of the current game, and enters a room with a transparent box filled with broken glass and a recording. It urges Strahm to have trust and to get into the box. He'll be hurt, but has a chance at life. Strahm shuts off the tape when he hears Hoffman walking in the distance. Shortly after, Hoffman walks into the room and Strahm then comes from behind and shoves Hoffman into the box and seals him in. Hoffman signals for Strahm to play the rest of the tape. The rest of the tape starts to play and explains the rest of the rules to Strahm, making him realize he would have lived if he had gotten into the box, stating that if he wouldn't, the room would become his tomb, and he would simply "vanish". The walls begins to close in on the room as the glass box lowers into the floor, safe from the enclosing walls. Strahm attempts to break into the glass box by shooting it and trying to pull it open, but the glass material is impenetrable, leaving Strahm on the outside to be crushed by the walls. Strahm starts shouting at Hoffman, "I know who you are!". Soon the walls come close enough for Strahm to attempt in climbing up to the ceiling and escape by the roof filter, but it is too late, and he becomes slowly crushed by the walls while Hoffman watches Strahm getting crushed from down below. With all evidence planted to frame Strahm for being the next Jigsaw accomplice, Hoffman is now able to continue his work as the next Jigsaw, undetected, leaving the Jigsaw legacy pinpointed at Strahm who is in fact dead.