At a quarantined university, a disparate group of students must band together if they are going to survive during a deadly viral infection outbreak.
A pre-med student and her friends encounter the death of a patient that exhibited symptoms of rabies. They are soon faced with an even bigger problem as their patient comes back from the dead and infects the people on campus, causing a lockdown and trapping the students inside.—Star Cinema
Several news reports that an unknown viral epidemic has been sweeping the Philippines. Meanwhile, Mario brings his daughter PJ, a medical student, to her first day in her senior year at San Lazaro University. Due to his previous work as an OFW and his inability to pay his daughter's tuition, Mario has a strained relationship with PJ, who is still traumatized from failing to save her mother from a fatal stroke. She reunites with her blockmates in Block Z: fellow med students and longtime friends Erika and Myles, and Block Z basketball team captain Lucas, who harbors feelings for PJ. Mario accidentally hits a pedestrian who secretly intended to scam him of money, but Mario instead brings the man to San Lazaro's hospital, where he meets with PJ again.
PJ and Erika are assigned to take care of Angie, a mother who has what appears to be a human bite in her leg. Angie suddenly has a seizure and dies shortly after, and PJ goes to comfort Angie's young daughter Ruby over her mother's death. Myles and fellow student Gary head over to bring Angie's body to the morgue, but Angie reanimates and bites Gary's neck, causing Myles to flee. Angie begins attacking other people in the hospital, causing others to be infected and reanimate as undead, forcing Mario and the pedestrian to flee together. The undead begins slaughtering several students and personnel around the university, including Lucas' team where he emerges as the only survivor. Lucas meets Mario and the pedestrian, but the latter had been bitten and turned, forcing the two to kill him. The two then separate, with both intending to find PJ. Student council president Gelo calls his general father for evacuation via helicopter on the hospital's helipad and tells his vice president Vanessa not to tell anyone as he only informed his father to make room for the two of them. Despite this, Vanessa secretly informs the university councilors to spread the word. Lucas manages to find PJ with Erika and Myles and the four work together to flee the school. The military quarantines the university, but they are forced to kill both zombies and students fleeing from the front gate.
Gelo confronts Vanessa for telling the university body about his helicopter, and Vanessa chastises him for looking out for himself when he has the resources to help everyone. They scuffle and Gelo accidentally pushes Vanessa off a staircase, killing her; when PJ's group stumbles upon the scene, Gelo lies and says she was infected and had to take her out in self-defense, and he joins the group. The group plans their route to the hospital, but when they become overwhelmed with zombies, they are rescued by Mario in the school's church. Mario has managed to hole up in the church with Ruby and security guard Bebeth. Gelo reveals that people have to be left behind as his helicopter can only fit two people, which angers the others in the process before the group convinces him that he needs them to survive.
The group passes by the faculty next, but when Ruby sees her zombified mother, she rushes to her and alerts the herd to their location. Ruby is devoured in the process, and the others are forced to leave when Gelo goes to the faculty and locks them out. The group temporarily rests in the dormitory, where they reminisce on their past and PJ and Mario reconcile, but a zombie attacks and bites Mario before it is killed. Mario tells the group to kill him to prevent him from turning, but the group opts to lock him inside the dorm's closet, and he says his final goodbyes to PJ before they leave him. Although the group manages to discover the zombies' weaknesses to headshots and water, their numbers begin dwindling: Myles is mortally wounded by a stray zombie and makes a last stand before he is killed, Bebeth stays behind fending off zombies from the others, and Erika sacrifices herself to let PJ and Lucas escape. The two manage to reach the hospital's rooftop, where Lucas lifts PJ to the helipad before using himself as bait to lure zombies away by jumping off the building.
A sorrowful PJ loses consciousness and awakens the next day with no helicopter in sight. She sees that she has a bite mark in her hand and realizes that she is immune to the virus, so she fights her way back to the dorms, killing several zombies including Angie in the process. PJ reunites with Mario, who is also immune, and the two decide to explore an ancient tunnel underneath the church that Ruby had previously discovered. There, they encounter Gelo, who is delirious from being infected and jaded from being seemingly abandoned by his father. The two manage to evade him and escape through a manhole and leave Gelo to be devoured by approaching zombies. PJ and Mario realize that the infection has spread beyond the university into the wider city, and they arm themselves.
News reports begin sharing the zombie's vulnerability to water. Bebeth broadcasts a message that she had survived. A large typhoon engulfs the Philippines, weakening and killing many of the undead in the process. Two weeks after the typhoon, a group of raiders discovers a heavily injured but still-alive Lucas, and their leader decides to take him in.
