The action of the film takes place between the events of the most famous and bloodiest parts of the cycle: SAW I and II. Suffering from cancer, John goes to Mexico to undergo an experimental treatment, which is his last chance to survive. After the procedure, he discovers that he has fallen victim to medical scammers who make a fortune from human suffering. They don't know that they have messed with a man who is an expert on suffering. John gets to work constructing a set of the most intricate, crazy and cruel traps you've ever seen. Doctors without a heart will be subjected to shock therapy, becoming the victims of the bloodiest revenge in the history of cinema.