Simone (Tanedra Howard) and Eddie (Marty Moreau), two predatory lenders, wake up wearing head harnesses with screws poised to their heads in a room with a caged-in scale in the center. They must tip the scale with some part of their own body to live. Simone chops her left arm off and tips the scale, saving herself. Lieutenant Mark Hoffman (Costas Mandylor) is called to the scene by Dan Erickson (Mark Rolston), who found Peter Strahm's fingerprints around the room. Erickson shows him that Lindsey Perez (Athena Karkanis) is alive despite the events that took place in Saw IV. Jill Tuck (Betsy Russell) meets with Hoffman at her clinic; he informs her that he is taking control of the games, and Jill hands him five envelopes from the box left to her in Jigsaw's (Tobin Bell) will.
William Easton (Peter Outerbridge), executive of a health insurance corporation, talks with his company's attorney, Debbie (Caroline Cave), about Harold (George Newbern), whose insurance policy was revoked after a discrepancy was found on his application and who later died from his illness. Later that night, William is kidnapped from his office and placed in a trap with a large vise enclosing his torso and an oxygen mask covering his face. Hank (Gerry Mendicino), his janitor and a smoker, is in the same situation across from him. Hank is killed when he fails to hold his breath longer. In the second test, Jigsaw's puppet informs William that he must choose to save either his file clerk Allen, who has no relatives, or his secretary Addy (Janelle Hutchison), who has family but is ill. William chooses to save Addy, and Allen is hanged by a barbed wire noose when his platform retracts. His third test takes place in a large boiler room. Debbie stands at the bottom of a caged-in maze with a device on her chest set to fire a spear through her head. At the end of the maze, she discovers through X-ray films that the key has been implanted in William's side and tries to attack him with a circular saw. She fails to get the key before the timer runs out and the spear kills her. In his final test, William finds his six staff members chained to a spinning carousel with a shotgun pointed towards each person, but he can only choose to save two of the six by pushing buttons in a device that will drive spikes into his hand and divert the shotgun upward. He reluctantly chooses to save Emily and Shelby.
Meanwhile, Erickson and Perez inform Hoffman that abnormalities were found in Strahm's fingerprints, and that the scrambled voice from the Seth Baxter tape did not match Jigsaw's. They lead Hoffman to the site where the voice is being unscrambled by a technician. The moment they discover it is Hoffman's voice on the tape, he kills all three of them and sets the room ablaze, using Strahm's hand to plant his fingerprints. Tara (Shauna MacDonald) and Brent (Devon Bostick) wake up in one locked cage, while reporter Pamela Jenkins (Samantha Lemole) wakes up in another. When Hoffman returns to the observation room, he finds a letter that Jill has placed on the desk, which he had written to blackmail Amanda Young (Shawnee Smith) in Saw III. Jill enters the room suddenly and gives Hoffman an electric shock. William simultaneously reaches the end of his path and finds himself between the two cages. It is shown that he and Pamela are brother and sister, while Tara and Brent are the family of Harold Abbott. Now they can choose to either kill William or set him free using a marked switch next to the tank. Tara cannot bring herself to end William's life, but Brent shows no mercy and shifts the switch to "Die". A platform of needles swings into William's back, pumping hydrofluoric acid into his body and killing him. Jill straps Hoffman to the chair and places a modified "Reverse Bear-Trap" on his head. She leaves Hoffman with a 45 second timer; he escapes the chair by breaking his hand. He stops the trap in between the bars on the door and pulls his head free, leaving one side of his mouth ripped open.