Saw

This grisly horror story plays out in a filthy bathroom, where two men awake to find themselves chained up. There is also a dead body, a gun, hacksaw and a dictaphone. They soon learn that they have been captured by a serial killer, who set up this situation for them: one of them has to kill the other within eight hours, or both will die. Only problem is, to reach the gun, one of them will need to saw off his foot...