Leo joins a squad of hardened mercenaries led by , who is desperate for redemption after the events on the ship. As they descend into the bunker, the "infection" changes. The possessed aren't just sprinting zombies anymore; they are melding together, forming massive, wall-crawling hive-minds that mimic the voices of the team's loved ones to lure them into the dark.

The story opens in New York City , now a silent, gray necropolis. Unlike the frantic shaky-cam of the previous films, the footage comes from a patchwork of sources: damaged NYPD body-cams, high-altitude military drones, and a handheld camera carried by a survivor named Leo , a former cameraman who worked for Ángela Vidal.

The Vatican’s "Special Operations" unit has realized that the virus isn't just biological; it’s an attempt by a primordial entity to rewrite the world. They believe the only way to stop the spread is to recover the "Genesis Strain" —the original bloodline hidden in a fortified underground bunker beneath the ruins of the Vatican’s secret archives in Manhattan.