Several years after the horrifying events at the Romanian abbey, Sister Irene continues her work within the church, haunted by her previous encounter with the demonic entity Valak. Her life takes a sharp turn when she's contacted by the now-adult Frenchie, who survived the same ordeal. Frenchie reveals disturbing occurrences in his small French hometown; people are vanishing, and an ominous presence looms. The previously sealed rift between the living and the damned seems to be cracking open, and Sister Irene's deep knowledge of the supernatural positions her as the only one capable of uncovering the truth behind the fresh surge of evil.

Joining forces with a skeptical yet determined local detective and a teenage girl with a curious gift for sensing the otherworldly, Sister Irene returns to the frontlines of the spiritual warfare. Venturing into the heart of darkness, this unlikely trio navigates a labyrinth of ancient catacombs, where they uncover a series of cryptic clues tied to Sister Irene's past encounters. They quickly realize the terror they face is far more sinister than an isolated haunting; an entire town is on the brink of being consumed by the unspeakable horror creeping through the shadows. As they draw closer to the source of the malevolence, the boundaries between the sacred and profane blur, and the true scope of their nightmare begins to reveal itself.