Rec 2

Picking up right where the first let off (with reporter Angela (Manuela Velasco) being pulled into the darkness by Nina Medieros - the girl who was first infected with the virus).

The story follows two groups of people - three thrill-seeking teens who follow a fireman and the father of one of the tenants into the building, and a squad of four soldiers who accompany Dr. Owen (Jonathan Mellor) - an official of the public health ministry - into the building to look for a vaccine. The first group is stuck in the building as it is under quanrantine, and the soldiers may only leave when Dr. Owen gives voice authorization.

It turns out that Dr. Owen is actually a high-ranking member of the Catholic Church who was working with one of the tenants, also a priest, to develop a vaccine for possession. Something went wrong which resulted in the release of a virus that transmits demonic possession to everyone who contacts it when exposed to the  blood or saliva of the infected. Dr. Owen hopes to find the initial infected girl, Nina Medeiros, in order to take a blood sample from her to continue developing the vaccine. In the end, almost everyone is killed but two of the teens (who are locked into a room for their protection from the infected), Dr. Owen, two soldiers, and Angela, who managed to escape from Medeiros in the first film. The group of four discover that Medeiros can only be found in total darkness, and cut all the lights to the penthouse where she was last seen by Angela.

After a long struggle, Angela ends up killing Medeiros by shooting her in the head with a shotgun. Dr. Owen still refuses to give the order to release them, and Angela goes crazy, killing the remaining soldier who survived the ordeal with Medeiros and beating Dr. Owen to near-death. As Dr. Owen lies bleeding on the floor, Angela reveals that she is actually the host for the demon, not Medeiros. She laughs at the thought that Dr. Owen almost let her free, but then tells him that she doesn't need his help anyways before killing him. She then takes his radio, and using her demonic powers to mimic Dr. Owen's voice, tells the people in charge of the operation that Angela is the sole survivor and should be released, that he, Dr. Owen, is infected and will stay behind, and to burn the building down. As the request is confirmed, Angela smugly walks towards the exit.

The last scene shows what happened to Angela after she was dragged into the darkness by Medeiros. After a brief struggle, Medeiros forced Angela's mouth open and vomited a giant parasitic organism (most likely the demon's actual form) from Medeiros' mouth into Angela's.

Order of Deaths: There are many deaths of the infected, including one whose head is blown off by a bottle rocket stuck in its eye

Thanks Evan!