Sam (Nicholas D'Agosto) has a vision of a horrible accident on a bridge, where all of his co-workers (including himself) are killed, except for his girlfriend Molly (Emma Bell).
As with the other films, all the characters start to die off in the order that they would have been killed in the accident had it not been prevented.
The new catch to the film is that if the intended victim kills someone else, then the death count remains the same, and that person's life will be spared.
Sam & Molly remain the sole survivors, and board a plane to France where he is beginning a cooking internship.... It turns out that this movie is a PREQUEL to the very first movie, and the plane that they get on, is the same plane that exploded in the first movie. Both are killed in the explosion.
Synopsis of the deaths:
As Silvermarc says, the new twist is the possibility that if the victims kill someone else they'll get to live out that person's remaining years. This seems to be proved correct when Nathan accidentally kills his antagonistic coworker, Roy, when Nathan's turn to die came up (Roy falls through a platform and gets his head caught in a hook in the factory). The reason it looks like Nathan has been saved is that Dennis (who was next in line) gets killed by the wrench immediately after Roy's demise--implying that death has skipped Nathan.
Peter becomes obsessed with killing someone else in order to live, but can't bring himself to kill an innocent stranger. He gets angry that Molly was actually supposed to live (she had managed to run to safety in Sam's vision in the beginning of the movie), and decides to kill her to claim the rest of her years. During their struggle Agent Block (Courtney B. Vance) shows up and is shot and killed by Peter. In order to eliminate any witnesses, Peter tries to kill Molly again. Sam saves her by stabbing Peter with the rotisserie spit.
At this point Nathan is still alive, so Sam and Molly are not the sole survivors (as Silvermarc says). As the prequel bit is revealed when Sam and Molly get on the doomed Flight 180 to Paris, Nathan arrives at a memorial service for Ray. There he discovers that an autopsy revealed that Roy had had a severely enlarged heart and only had a matter of days to live anyway. Nathan realizes that he hasn't been given the second chance at life he had thought he was getting, just as Flight 180 explodes in the sky (with Sam and Molly on it) ... and a giant piece of equipment falls through the roof of the bar, crushing Nathan.
Thanks Silvermarc and Greg B!