Between the events of 'Saw' and 'Saw II', a sick and desperate John Kramer travels to Mexico for a risky and experimental medical procedure in hopes of a miracle cure for his cancer, only to discover the entire operation is a scam to defraud the most vulnerable. Armed with a newfound purpose, the infamous serial killer returns to his work, turning the tables on the con artists in his signature visceral way through devious, deranged, and ingenious traps.

Exasperated at being stuck on a piano Rhapsody he's been writing for seven years, Sol pushes himself over the edge, having an hallucination of a mysterious young woman. Soon, Sol discovers that he has brain tumors, and a risky operation is his only means of survival. Initially deciding to go through with the surgery, things change when he meets Sofia, the woman from his vision. She urges Sol not to have the operation because the tumors aren't what they seem. Unable to fathom her strange appearance, he starts out to discover the nature of these events - unearthing what The Rhapsody really is.