The film centers on Brian, a medical courier, as he navigates a zombie apocalypse, tasked with transporting a vital component for a T-Virus antidote. The narrative takes a personal turn when Brian himself becomes infected. As he nears the scientists developing the cure, the T-Virus begins to transform him into a monstrous entity. Despite this horrifying metamorphosis, Brian retains fragments of his humanity, desperately pleading for the cure even as he inadvertently harms the scientists. This sequence is particularly poignant, as the audience witnesses the tragic struggle of a character they've come to know succumb to the virus.

During an interview, Cregger and actor Austin Abrams discussed the original ending, where the cure was destroyed prematurely, leading to Brian's swift and complete transformation into a monster. Cregger admitted that Brian's rapid loss of humanity was a misstep in the initial script. Fortunately, Cregger had filmed contingency shots, including one where a scientist discreetly pockets the cure. This allowed the team to re-edit the film's climax, preserving Brian's desperate fight for survival and maintaining audience investment in his fate until the very end, thus amplifying the film's tragic undertones.

The altered ending significantly contributed to the film's emotional depth, transforming it into a poignant tragedy rather than a mere horror spectacle. While Cregger had initially considered the film a standalone project, he remains open to the possibility of a sequel, having already conceived ideas for future installments. Although his next directorial endeavor will be unrelated to the Resident Evil universe, he acknowledges that the future holds endless possibilities for his involvement with the franchise, hinting at a potential return to its thrilling world.