Wikipedia
"A man named Seth (Joris Jarsky) is in a trap which has a pendulum blade suspended above his body. Seth was a murderer released early from a life sentence on a technicality. He is told to push buttons inside of two devices, his hands will be crushed but the pendulum will be stopped. Reluctantly he does push the buttons but the pendulum descends upon him regardless and cuts him in two, meaning the trap was inescapable, and therefore not one that had been set by Jigsaw (Tobin Bell).
In a scene from the end of Saw IV Agent Strahm (Scott Paterson) enters the room where Jigsaw died and shoots Jeff Reinhart (Angus Macfadyen) dead in self-defence. Seconds later, someone locks the door on Strahm. He exits through a secret door, and finds a recorder. The recording warns him he can find salvation or die in the room, and urges him to make the right choice. He disregards it and is attacked by a figure in a pig mask. He wakes up in one of Jigsaw's traps and finds his head in a sealed box, which quickly starts to fill with water. Before he runs out of air, he performs a tracheotomy with the tube of a ballpoint pen. The police make it to the Gideon warehouse, and Hoffman (Costas Mandylor) emerges carrying Corbett Reinhart (Niamh Wilson), claiming that he saved her. Strahm is carried out on a stretcher alive but badly injured. The Chief of Police announces that the Jigsaw murders are over. Jill Tuck (Betsy Russell) is given a videotape and box from John's lawyer. The contents of the box, says John, are of grave importance to her. After looking in the box, Jill leaves without telling John's lawyer what's inside.
Agent Perez (Athena Karkanis) dies from her wounds sustained from a Jigsaw trap in Saw IV, and Strahm tells Hoffman that her last words were his name. Strahm returns to his office and begins to investigate all of the victims linked to Jigsaw, discovering that Seth murdered Hoffman's sister and theorizing that the trap for Seth was made by Hoffman. Strahm guesses that Jigsaw used this fact to blackmail Hoffman into helping him, and in flashback we see Hoffman help Jigsaw set up Paul Stallberg (Mike Butters) in the razor wire trap in Saw, set up the gas house in Saw II, and talk with Jigsaw before leaving him with Lynn Denlon (Bahar Soomekh) and Amanda (Shawnee Smith) in Saw III.
Five people wake up in a sewer, in a trap connecting all five to guillotine blades, keys are in glass boxes at the other end of the room. Mallick (Greg Bryk) gets anxious and runs ahead, starting the timer. Charles (Carlo Rota) pulls the cord causing Mallick to fall to the ground. Mallick pulls the cable hard causing Ashley's (Laura Gordon) cable to pull her back. The timer runs out and Ashley is beheaded..."
LA Times
Labyrinthine and torturous, the "Saw" series increasingly has come to resemble the baroque booby traps laid by its serial-killing mastermind, Jigsaw (Tobin Bell). In the fifth installment, the cops investigating the case have all been bumped off, with the exception of Scott Patterson's dogged FBI agent and Costas Mandylor's lone detective.
The latter, as those who've been following along will recall, is now the sole bearer of Jigsaw's grisly legacy, although the fact that Bell's character had his throat slashed at the end of Part 3 hasn't prevented him from showing up in the sequels.
He might be dead but he apparently left behind enough machinery to extend the franchise ad infinitum.
The virtues of the individual films are almost beside the point, since it's hard to imagine why anyone would want to pick up the thread at this late date, but "Saw V" is a particularly dull and discombobulated affair, shot and acted with all the flair of a basic-cable procedural. Patterson and Mandylor are so wooden that their cat-and-mouse game has all the excitement of watching dust bunnies swirl in an air current.
Even if you don't enjoy watching hapless innocents die in inventively gruesome ways, it's a relief when the movie cuts away to the five people trapped in a series of "tests," which inevitably involve mutilating themselves (or others) to stay alive.
NY Times
It would be nice to be able to say that “Saw V” is a revolting, nerve-racking trip into the cesspool of the human imagination, since that seems to be the point of this undying horror franchise. Sadly, the latest and least of the “Saw” films is just plain boring and even a little tame — albeit by the standards of a genre that helped bring the phrase “torture porn” into the lexicon.
Directed by David Hackl from a screenplay by Patrick Melton and Marcus Dunstan, “Saw V” makes the fatal mistake of taking itself way too seriously. Like a once-popular TV show that degenerates, in its final season, into self-involved soul-searching of interest only to the most devoted, trivia-obsessed fans, the movie seems to think that people care about the “Saw” mythos, as opposed to the “Saw” method of preposterously baroque killing for kicks.
Picking up where its predecessor left off, the new film devotes most of its time and energy to a pair of the dullest characters in the history of horror: the law enforcement agents Hoffman (Costas Mandylor) and Strahm (Scott Patterson). Having survived the shenanigans of the psycho known as Jigsaw, they now find themselves enmeshed in the antics of a laughably convoluted plot that skips back and forth in time, trying to piece together who did what, when and why. The only question really worth asking here: Who cares?
Entertainment Weekly
Saw V is dead on the table. The franchise, a gross-but-intermittently-clever blechfest that went totally splat about midway through Saw III, now just piles on the graphic torture sequences, but by now every twist of the stomach and the plot feels telegrammed. Even though he ''died'' two movies ago, Jigsaw (Tobin Bell) returns, as the saga's storyline snakes around itself in ever more laughable circles, just to keep generating sequels. Meanwhile, the production values have become so horror-movie shoddy that Saw V has more in common with kitsch like Friday the 13th Part V than the original Saw.