This sequel to QUARANTINE (which was a remake of REC) takes place during and after the events of that first movie. The story first focuses on two stewardesses who have the night shift. Right after a hugely obese guy is bitten by a rat he begins to go berserk and endangers the plane and bites one of the stewardesses in the face. He's overpowered by the passengers. But the copilot is sick and they have to make an emergency landing. Once they land, however, they are locked into a section of the airport and surrounded by the military. They learn that this infection started in an apartment building in Los Angeles and somehow got on the plane. Basically, they all have to somehow survive as they become infected, one by one. Even an old guy with Parkinsons Disease becomes a raving lunatic.
I suspected who the culprit was in the first ten minutes of the movie and I don't think you'll be at all surprised about this revelation. As sequels go this is a good one and I can see this being a decent enough DVD movie series (anything is better than CHILDREN OF THE CORN!). If you liked the first one you'll like this, though it's one of those "zombie" flicks like 28 DAYS LATER or THE CRAZIES, where they're really not dead zombies but diseased people. Recommended.