Minutes after Amanda Young abandons Detective Eric Matthews in the underground restroom at the close of Saw II, he manages to escape by breaking his foot against a toilet lid, slipping free from his ankle chain. Six months later, Lieutenant Rigg, along with Detectives Kerry and Hoffman, discover another victim of Jigsaw's cruel games. In a harrowing test, Troy finds himself forced to rip chains from his own body to escape an inevitable bomb. Tragically, the door leading out is sealed, making his situation utterly hopeless and diverging from Jigsaw's usual method of offering a chance at survival.
Feeling the weight of guilt from Matthews’ mysterious disappearance, Kerry awakens to find herself ensnared in a horrifying harness that pierces her ribs. A key necessary for her escape lies within a vessel of acid. Despite her efforts to secure the key, the device mercilessly tears her rib cage apart, rendering her plight no less inescapable.
Meanwhile, Jeff, played by [Angus Macfadyen], is a man engulfed in the flames of vengeance after the tragic loss of his son. Alongside him is Dr. Lynn Denlon, portrayed by Bahar Soomekh, whom John Kramer, the mastermind behind these gruesome tests, has also kidnapped. Lynn finds herself brought to John, who is now bedridden and battling cancer, by his apprentice Amanda. Lynn is presented with a grim ultimatum: keep John alive throughout Jeff's trials, or face lethal consequences from the collar strapped around her neck, which will discharge a volley of shotgun shells if she fails.
Amidst this chaos, Jeff awakens in a derelict meatpacking plant, soon learning that several trials await him, each one designed to lead him to "the man responsible for the loss of his child." As the cruel games begin, Jeff is thrust into a series of sadistic challenges that force him to confront the witnesses and perpetrators of his son's wrongful death.
In his first brutal test, Jeff encounters Danica, an essential witness to the drunk-driving incident that claimed his son's life. She has become a target of his wrath for her refusal to testify. Bound and exposed to the unforgiving cold, Danica persuades Jeff to aid her, though her freezing body prevents him from retrieving the key she needs for escape.
His subsequent challenge takes him to Judge Halden, who previously sentenced his son's killer to a mere six-month prison term. To save Halden from a grotesque fate, Jeff sacrifices childhood mementos to retrieve the key, further stoking his desire for revenge.
In the penultimate test, Jeff faces Timothy Young, the man who took his son's life. Timothy is gruesomely restrained in a contraption that will methodically shatter his limbs. As Jeff frantically tries to save him, a tragic accident leads to Timothy's demise just as Jeff retrieves a critical key.
Throughout this turmoil, Lynn and Amanda fight to sustain John’s life. An intense moment arises during a makeshift brain surgery when John expresses feelings for another woman, misinterpreted by Amanda as affection for Lynn. Under the pressure, Amanda's emotional state unravels, revealing her own dark history and the psychological toll it has taken on her.
After a fervently complicated conversation with Lynn, Amanda divulges that Jeff's meticulous tests were specifically designed to be inescapable. When news arrives that Jeff's trials are complete, Amanda’s unwillingness to believe in the potential for change leads her to make a tragic decision. Just as both their fates intertwine, violent confrontations unfold leading to devastating realizations about sacrifice and betrayal.
In a heart-wrenching climax, when Jeff arrives to save Lynn, Amanda is shot and dies in the hands of her own design. Finally, John, facing his own mortality, presents Jeff with a cruel choice: exact revenge by killing him or finding the strength to forgive. Ultimately, Jeff’s decision leads to a catastrophic conclusion where vengeance and fate intertwine, leaving him faced with the grim reality of failure, loss, and the chilling legacy of John Kramer.
