Saw

The movie starts with a man waking in a bath-tub filled with water. He sits up, not noticing that as he does, he pulls the plug out, and something that was floating above him goes down the drain.
He gets out and starts shouting for help, until he hears another man in the room with him. The man finds the light switch and turns it on. The two men see in the middle of the room, a dead man, with a gun in one hand and a tape recorder in the other. He has recently blown his own brains out.
The two men make more talk on who they are - the man in the bath-tub's name is Adam (Leigh Whannell), and the other man is Dr Lawrence Gordon (Cary Elwes). Neither remembers how they got there. Each of them is chained to a pipe, at opposite ends of what looks like a bathroom. There seems to be no way out - Lawrence tries and fails to open a door.
After a while they each find in their pockets a tape. Lawrence also finds a bullet and a key with his - both men try and fail to unlock their shackles with it. Adam constructs a reaching device from his shirt and the plug from the bath to hook the tape recorder out of the man's hand, and play his tape on it. A distorted voice tells him he's part of a game, and he may end up dead unless he plays along. Lawrence throws Adam his tape, which tells Lawrence that he has until 6 PM to kill Adam, or his wife and daughter will die. Right at the end of it, he can hear the voice whispering 'Follow your heart.'
Lawrence notices a heart drawn on the toilet tank, in which Adam finds a black bag containing 2 saws. He throws one to Lawrence and both men attempt to saw through their chains. Adam's saw breaks, and Lawrence realises that the idea is for them to saw through their legs. He tells Adam he thinks they have been captured by the Jigsaw killer, and that he was once a suspect.
The movie flashes back to several cops, Detective Tapp (Danny Glover), his partner Detective Sing (Ken Leung) and some others. They are at a murder scene, being told by a cop named Kerry (Dina Meyer) exactly what happened. A man was trapped in the middle of the room, surrounded by barbed wire. There is another flashback; we see the victim wake up in the room, and told by the same voice from the earlier tapes that if he wants to escape, he has to find a path through the barbed wire before the door to the room locks in 2 hours. Evidently the man didn't make it through the wire - he is hanging from it, cut to pieces. We then see another victim, a man who was incinerated after a candle caught fire to the flammable liquid he was covered in, while he was trying to find on the wall of the room he was in a safe combination (the safe containing the antidote to the poison in him). Kerry tells Tapp and Sing they found a peep hole at the scene, indicating the killer watches his victims. They also found a pen-light, which they conclude belongs to Lawrence.
Lawrence is brought in for questioning while he is at work in a hospital. He angers an orderly named Zep concerning a dying patient named John (important). At the police station, Lawrence tells the police he was with someone else the night the incinerated man died. Tapp brings in a woman who survived her run-in with Jigsaw and makes her tell Lawrence her story. A further flashback shows the woman, Amanda (Shawnee Smith) wake up in a room with a device fitted to her face. A TV next to her shows a creepy clown puppet tell her that the key to the device is in the stomach of the dead man in the cell with her, and if she doesn't unlock it within a minute, the device will explode and rip her face apart. She gets up (which starts the timer) and finds a knife next to the man - who is actually not dead, and wakes up. Amanda stabs him and cuts him open, sifting through his guts until she finds the key, unlocks the device and throws it on the ground, just as it explodes. Lawrence, meanwhile, is let go.
This is where I can't really remember the order. We go back to Adam and Lawrence. After realising the mirror in the room is 2-way, they smash it and find a camera behind it, through which Jigsaw is watching them. Lawrence tells Adam about his family. There's a flashback to the last time Lawrence saw them - his daughter Diana (Makenzie Vega) thought there was someone in her room. Lawrence searched the room for her and after finding nothing, gets paged by 'work' (actually the med student he's having an affair with) and has to leave, not before arguing with his wife Alison (Monica Potter). Back in the room, Lawrence shows Adam pictures in his wallet of Diana. Adam finds a polaroid of Diana and Alison tied up and gagged, with the message on the back 'X Marks the spot, sometimes you see things better with your eyes closed.' Adam hides the picture and throws the wallet back to Lawrence.
Another flashback shows that just after Lawrence left for 'work,' Alison goes to Diana's room and finds a man covered in a sheet attacking Diana. The man knocks them both out, ties them up and gags them.
There is a flashback to Tapp and Sing still trying to solve the case. Tapp watches the video that Amanda saw, hearing a fire alarm in the background and seeing grafitti on the walls. Using this, the men track down the building it was filmed at. When they get there, they find a model mock-up of Adam and Lawrence in the room, the clown puppet and a pig's head mask. They also find a man, still alive, strapped into a chair with a drill on either side of his head. Tapp and Sing hide when they hear the killer, dressed in a cloak, come up the stairs. Tapp and Sing leap out at him, but the killer pushes a button that starts the drills and tells them there are a bunch of keys in the box next to them - one of them will release the man. Sing tries to unlock the man, while Tapp attempts to arrest Jigsaw. Sing eventually shoots the drills, saving the man - and Jigsaw slashes Tapp's throat, escaping. Sing chases and shoots him, but trips a wire that sets off several other guns, killing him. Jigsaw gets up and walks away.
Back with Adam and Lawrence, Adam tells Lawrence to turn the lights out. When he does, a glow-in-the-dark X can be seen on the wall behind Lawrence. He smashes through the tiles and finds a box, using the key from earlier to unlock it. Inside is a mobile/cell phone (which can only receive calls), a note, 2 cigarettes and a lighter. Adam asks for the cigarette, as Lawrence reads the note, which basically says that the dead man in the room had poison in his blood, and if Lawrence dips the cigarette in it and gives it to Adam, he will himself be poisoned. The phone rings; it's Jigsaw forcing Diana and Alison to speak to Lawrence. Alison tells Lawrence not to believe anything Adam says, and that he already knew him. The phone goes dead and Lawrence questions Adam. It turns out Adam was being paid by Tapp (who survived) to follow Lawrence and take photos of him. We flashback to very creepy scenes showing how Lawrence and Adam were captured by Jigsaw.
Somehow, Lawrence works out that Zep, the orderly from before, is Jigsaw. He tries to trick Zep, by dipping one of the cigarettes in the blood, then turning the lights out and whispering to Adam to play along. He turns the lights back on and offers Adam a cigarette, giving him the unbloodied one. Adam smokes it and pretends to die - however, he screams when he is electrocuted through his shackles. He and Adam realise it's 6 PM, and Zep goes to kill Diana and Alison, who have managed to free themselves. Zep phones Lawrence, who freaks out when he hears Alison and Zep fight and scream. Suddenly, Tapp, who was discharged from the police after the investigation into Jigsaw drove him crazy, and had been watching Lawrence's house through a surveillance video, appears and gets into a shoot-out with Zep. Alison and Diana escape. Zep runs out of the house and Tapp chases.
Lawrence meanwhile has completely lost it; believing his family has been killed, he saws his own foot off, crawls over to the dead man's gun, loads it with the bullet and shoots Adam. Outside the room, Zep and Tapp are in a tussle - Zep shoots Tapp, killing him. He opens the door to the room, and is about to kill Lawrence when Adam grabs him and beats him over the head with the lid of the toilet tank, killing him. Lawrence tells Adam he will go for help, or they'll both bleed to death. He crawls away, and just after he does, Adam finds a tape recorder on Zep. The voice on the tape is that of Jigsaw - telling Zep that to get the antidote for the poison in him, he will have to set up the situation with Lawrence, his family and Adam. Behind Adam, the 'dead' man suddenly stands up, pulling a mask off, and revealing himself to be John, the patient from earlier. He electrocutes Adam when he tries to shoot John, and walks out the room, slamming the door shut again, and leaving Adam screaming in the dark.