Just because John Kramer (Tobin Bell), aka "Jigsaw," the fiendish serial-killing game-player of the previous three SAW movies, was nearly decapitated by a buzz saw at the end of SAW III doesn't necessarily mean he's gone for good. In the world of horror-movie franchises, no one's really dead until well after the series starts going straight to DVD. That writers Patrick Melton and Marcus Dunstan have found a way to keep Jigsaw among the dying should please die-hard fans, but those of us who quickly tired of the grisly fun and games midway through SAW II will resent the unnecessarily convoluted plotting and storylines that require a master's degree in SAW studies to make any sense. Make no mistake, Jigsaw is dead — his particularly gruesome autopsy opens the film — but he hasn't yet played his final hand. Deep in his stomach, the coroner finds a cassette tape that Jigsaw managed to swallow before he was killed at the end of SAW III. The recording hints that yet another game is on, this time involving the last surviving investigator, Detective Hoffman (Costas Mandylor), and Rigg (Lyriq Bent), a SWAT commander with a savior complex. After he's knocked unconscious in his home by a sinister figure in a pig mask, Rigg is treated to a trademark Jigsaw video proving that detective Eric Matthews (Donnie Wahlberg), who has been missing for the past six months and is presumed dead by everyone but the never-say-die Rigg, is not only still alive but caught in one of Jigsaw's fiendish death traps: He's shown teetering on a block of quickly melting ice with an ever-tightening manacle clamped around his neck. Strapped to the chair next to him is Detective Hoffman. Rigg has 90 minutes to find them, after which time Matthews will strangle and Hoffman will be electrocuted in the puddle of melted ice. But, the voice of Jigsaw warns, Rigg must not let his impatient, impetuous nature get the better of him, and Rigg is put through a series of "games" that require him to make difficult moral choices that challenge his instinct to save as many people as he can. Meanwhile, FBI special agents Strahm (Gilmore Girls's Scott Patterson) and Perez (Athena Karkanis) pick through the remains of serial-killer expert Kerry (Dina Meyer), who had her rib cage torn open midway through SAW III, and realize that the terminally ill Jigsaw must have had a third accomplice assisting him. Jigsaw was far too weak, and crazy sidekick Amanda Young (Shawnee Smith) too small, to hoist Kerry into the elaborate contraption that eventually killed her. Could there be yet another accomplice out there helping Jigsaw continue his work as a self-help sadist from beyond the grave? In a series that's running out of ideas, anything's possible. The SAW franchise is unique in that it develops its sequels by looking backward, retroactively introducing new characters through flashbacks, filling in old plot holes with new twists and revelations, and piling on more and more backstory. This time out, we learn about John Kramer's relationship with Dr. Jill Tuck (Betsy Russell), and the tragedy that got him started on his mission to help people help themselves by torturing them to death. The trouble is that if you haven't seen the other entries in the cycle, or don't have all the characters committed to memory, you'll have trouble figuring out who anybody is or, in the end, what any of it is supposed to mean.