Jigsaw begins his killings again, and at the scene of one of his "games" he leaves a note calling for a Detective (Eric) Matthews. At first reluctant to get involved, after Eric notices a clue Jigsaw left behind and works out the location of his hideout, he decides to come along for the ride when a SWAT team break in. Jigsaw or "John" rather (Jigsaw being a name given by the press) is actually inside, sitting at his desk and attached to a life support system (he is already dying of cancer.) It's at this point he reveals that he has trapped a group of people in a house somewhere, (including the heroine addict from the first movie, Amanda) and they have 2 hours to live before a nerve gas filling the house causes them to bleed to death.
There are several doses of the cure hidden in the house but in order to get them they will have to pass a series of brutal tests. Eric and the team can watch the different rooms of the house through monitors in Jigsaws base and can see the 2 hour timer ticking down but have no way to communicate with the people inside, and to his horror Eric realises one of the people is his son, Daniel. John challenges Eric to a game. The rules of the game are simple. He has to sit and listen to what John has to tell him, only then will he see his son alive ever again. As the unlucky people in the house begin to explore and die one by one, time is ticking away and Eric seems no closer to saving his son.