[REC]2 picks up the storyline just after the end of the first film, with everyone seeming to be dead or possessed in the apartment building. The building had a laboratory in the top floor, which seemed to be working on a toxin that causes demonic possession. Even worse, this seems to be contagious upon bite, and the apartment is filled with these demonically possessed, zombie-like undead.
Pushing the storyline further into the medical science and religious reasoning of the demonic contagion, [REC]2 also pushes further away from the American remakes. These films stick with a human rabies explanation, whereas the original Spanish franchise is more fittingly concerned with issues of faith and demons. The demon virus does even more damage this time, even when a highly armed S.W.A.T. team arrives.
Even with guns and special equipment, these men are once again trapped inside the building in quarantine until they accomplish their goal. The mission they have is where the film takes a slight drop, but the terror of the situation still remains. The element of footage from cameras making up the film also remains, with several different cameras this time. Additional ones are added in with the arrival of a few kids who managed to sneak in. There are a lot of scares in this sequel, maybe even more than the first film, but the simplicity and mystery of the first one will always far outweigh the quality of the sequel.