The main problem with the film is the final act, which has needless references to the original “Saw”, and a supposed twist ending which has been clearly signposted throughout. As well as being frustratingly obvious, the ending plot twist smacks of the worst kind of cynicism, and serves only to undermine the film’s bleak theme of hopelessness, leaving the viewer with a frustrated feeling of being sold down the river. Although the ending does undo much of the good work which has gone before, “Saw 2″ remains a film which exceeds expectations, and certainly stands above most modern genre efforts. Full-blooded and fast paced, it offers genre fans a solid slice of distinctly adult horror, and one which, however clumsily, at least attempts to employ cerebral as well as visceral shocks in its brand of madness.

Jigsaw is back. When a new murder victim is discovered with all the signs of Jigsaw's hand, Detective Eric Matthews begins a full investigation and apprehends Jigsaw with little effort. But for Jigsaw, getting caught is just another part of his nefarious plan. Eight more of his victims are already fighting for their lives and now it's time for Mathews to join the game.

Adam Stanheight (Leigh Whannell), a photographer, and Dr. Lawrence Gordon (Cary Elwes), an oncologist, awaken at opposite ends of a disused bathroom, Adam in a water-filled bathtub. Both men are chained at the ankle to the pipes. Lying between them is a corpse in a small pool of blood holding a revolver and a microcassette recorder. Adam and Lawrence discover tapes in their pockets; the men learn from both tapes that Adam must escape the bathroom, while Lawrence must kill Adam before six o'clock, or he'll lose his wife and daughter and be left to die. They find a bag containing two hacksaws, though neither is able to cut through the chains. Adam breaks his saw and throws it at a mirror in frustration; Lawrence realizes that the saws are meant to be used on their feet.
Lawrence tells Adam that their captor is the Jigsaw Killer, who places his victims in situations or traps, referred to as "games", in which they must be put through physical and/or psychological torture to survive and escape with a better appreciation for life. Flashbacks show that while Lawrence was talking with some students and an orderly named Zep Hindle (Michael Emerson) about the terminal brain cancer of a man named John Kramer (Tobin Bell), he was approached by Detectives David Tapp (Danny Glover) and Steven Sing (Ken Leung) about his penlight being found at the scene of a Jigsaw "game". He viewed the testimony of Amanda Young (Shawnee Smith), a heroin addict, who is the only known survivor of Jigsaw's games; she barely escaped from having her jaw ripped open during her game by a "Reverse Beartrap" and believes that her experience made her a better person. Other victims of Jigsaw's games included Paul (Mike Butters), who was trapped in a cage filled with razor wire, and Mark (Paul Gutrecht), who was trapped in a room with a flammable substance all over his body along with a candle to help him read the walls covered with numbers that hid the combination to a safe. One of the detectives revealed that Jigsaw frequently watched his victims die — he "liked to book himself front row seats to his own sick little games".
Meanwhile, Lawrence's wife and daughter, Alison (Monica Potter) and Diana (Makenzie Vega), are being held captive in their home by a man who is watching Adam and Lawrence through a camera behind the bathroom's mirror while tormenting Alison and Diana. Their house is simultaneously being watched by Tapp, who was discharged from the force. Flashbacks show that he became obsessed with the Jigsaw case after viewing Amanda's testimony, and that he and Sing illegally entered a warehouse they knew to be Jigsaw's lair and saved a man from being killed by drills aimed at his neck. Jigsaw managed to make a run for it after slashing Tapp's throat, and Sing was killed by a shotgun booby trap while pursuing him. After being discharged, Tapp began stalking Lawrence.
In the bathroom, Lawrence finds a cigarette, a lighter, and a mobile phone that can receive calls but not make them. He and Adam use the first two items to try to stage Adam's death, but an electric shock through Adam's ankle chain foils this plan. Following these events, Adam and Lawrence recall their abductions; they were both ambushed and knocked unconscious by a stranger wearing a gruesome pig mask. Lawrence receives a call from Alison, who warns him that Adam knows more than he is telling. Adam explains that he was paid to take pictures of Lawrence for the past few days by Tapp, and shows Lawrence a pile of pictures of him from the bag containing the hacksaws. Lawrence berates Adam for invading his privacy, while Adam shows Lawrence evidence that he was cheating on Alison. Adam then notices a picture of a man in Lawrence's house; Lawrence identifies the man as Zep Hindle, and the two deduce that Zep is their abductor. Adam then points out that it is six o'clock, the deadline. Zep moves to kill Alison, but she frees herself and manages to overpower Zep, gaining Tapp's attention in the process. He arrives in time to save Alison and Diana from Zep, allowing them to escape, and chases Zep to the sewers.

I loved watching this film! This movie was the second part of Jig saw excellent master plan of making people evaluate their life to realize what they have in their life and to see what they would do to stay alive. But in this one all they had to do was put their head together.

I love watching this movie! Love the ending to always good to hear someone screaming!