In a quarantined apartment building, a Ministry of Health official, Dr. Owen, leads a heavily armed GEO team—Fernandez, Martos, Rosso, and Larra—on a mission to uncover what happened to the inhabitants who have become infectious and violently aggressive due to a deadly virus. Equipped with video cameras and body cams, they proceed with caution, and the tension in the building is palpable as they move from floor to floor, their lights slicing through the darkness.
They reach the attic, only to find it unoccupied, which adds a layer of mystery to the already perilous situation. On their return to a lower level to investigate a disturbance, they are ambushed by infected residents, forcing them into a rapid, brutal adjustment to the new threat. The encounter grows personal as Martos is infected, and Owen must improvise a way to hold back the threat long enough to regroup. In a tense moment, Owen uses a religious mantra and a rosary to keep the danger at bay inside a room, revealing a deeper motive behind the mission that goes beyond a routine health check.
The situation escalates when Owen reveals a startling truth: he is not just a health official but a priest sent by the Vatican to obtain a blood sample from a possessed girl named Tristana Medeiros, who is identified as the source of the infection. The GEO team searches the apartment where Medeiros was kept and discovers the lifeless body of Father Albelda, the priest initially charged with Medeiros’s case. They also recover a blood sample from Medeiros that had been taken by Albelda, only to lose it again amid the chaos. With the clock ticking, the plan shifts toward obtaining a blood sample directly from Tristana. The danger intensifies as the group is attacked by more infected, and tragedy strikes when Larra, cornered, takes his own life.
Meanwhile, a father—whose infected young daughter Jennifer is among the victims—persuades a firefighter to infiltrate the building through the sewers. They are unknowingly followed by three teenagers, Tito, Mire, and Ori, and the police seal their escape route. Jennifer’s father is infected and killed by the GEO team, while the firefighter is killed accidentally by Mire, who also kills Martos. After Tito becomes infected, the crew confines Mire and Ori to a room, and they encounter the journalist Ángela Vidal, who is shocked but safe. The team interrogates Tito and, through his cryptic responses, begins to suspect that Medeiros is somewhere in the penthouse, with certain parts of the building accessible only in total darkness or with infrared light.
Using the night-vision on Ángela’s camera, they discover a hidden door and press forward. They are confronted by Medeiros, who kills Fernandez and wounds Owen. In a desperate moment, Ángela Vidal fires a shotgun and eliminates Medeiros, but the win is short-lived. Owen, furious at the loss of the blood sample and the growing threat, refuses to authorize their exit. In retaliation, Ángela strikes back, killing Rosso when he tries to step in. The team soon discovers that the demon possessing Tristana has now possessed Ángela herself, twisting her into a conduit for the malevolent force.
In a chilling turn, Ángela kills Owen and imitates his voice to contact the authorities, claiming that the mission is complete and the only survivor allowed to leave is Ángela herself, who must stay inside due to the infection. A flashback then reveals what happened just before the film’s beginning: Ángela was captured by Medeiros and had a vermiform organism transmitted to her. As the response team arrived on the scene, Ángela went into hiding, her fate now sealed by the possession that has overtaken her.
- The haunting tension remains, as every door and corridor becomes a potential trigger for violence, and the line between salvation and damnation blurs in the darkness. The story folds back on itself in a grim revelation: the mission’s supposed success has a cost beyond the immediate danger, leaving the viewer with a chilling portrait of possession, coercion, and the fragility of human resolve in the face of an unstoppable contagion.