Jigsaw has escaped again for Saw 3, after he escaped at the end of Saw 2 he has apparently become moch more afflicted by his cancer, and is fighting to survive. A doctor is kidnapped, and she is asked to play a game. As long as she keeps jigsaw alive while another player in a seemingly unrelated game completes his tasks, the doctor will live. Shes hooked up to a heart rate trigger, which will detonate if jigsaw dies, and is forced to take care of him. Surgical tools are not the greatest, but a power drill and a bonesaw can do wonders under pressure.
The man playing the other game has a chance to get vengance on a man who killed his child in a car accident, and also on the judge who didnt convict him.
He meets 3 people on his trip, and gets clues to his game as he goes, unwrapping the subplot as the main story is told.