In 1952 Romania, a young nun at a secluded abbey takes her own life, leading the Vatican to investigate the mysterious circumstances surrounding her death. Father Burke, a seasoned demonologist with a haunted past, is dispatched along with Sister Irene, a novitiate on the verge of her final vows. Plagued by visions and holding a strong faith, Sister Irene is thought to have a connection to the otherworldly events at the abbey. The pair arrive in the remote castle with the guidance of Frenchie, a local villager who discovered the nun’s body.

Once at the abbey, they encounter an unnerving silence and a sense of evil hanging in the air. As Father Burke and Sister Irene explore the ancient halls and burial grounds, they unearth the abbey’s ungodly secret—a malevolent entity known as Valak. The demon has taken the guise of a nun to cover its own hideous form and is spreading its influence beyond the sanctified walls. Their faith and strength are pushed to the limit as they face the unholy force that seeks to prey on their fears and endanger not only their lives but their souls.