Plot

As Alyssa and Karla try to escape from the church home that holds them captive, Karla is slaughtered by a vicious, semi-human creature.

Ever since that close encounter with a monstrous abomination, Father Peter has dedicated himself to God, giving his all to help young women get their lives back on track at the St. Matthias House of Rehabilitation. However, the pious servant is shocked to discover that troubled halfway house residents Alyssa and Karla have gone missing. Now, to shed light on their unaccountable disappearance, disgraced Detective Robbie Kimball embarks on a mission to find them, unaware of the risks involved. Indeed, truth is sometimes stranger than fiction, as someone, or better yet, something, spills innocent blood. Who knows what's been happening behind the closed doors of the mysterious Amityville institution?—Nick Riganas

Halfway house residents Alissa Nolan and Karla Montgomery attempt to escape the nightly lockdown at Saint Matthias House of Rehabilitation. A werewolf attacks and kills Karla while Alissa flees outside.

An Internal Affairs director assigns disgraced detective Robbie Kimble to investigate the disappearances of the two women. At Saint Matthias, Robbie meets Father Peter, Sister Ruth, new priest Father Michael, and several female residents. Robbie gets a tip that Alissa may have gone back to The Penny Whistle, a biker bar she used to work at in Levittown.

The two priests host group therapy for residents Nikki, Iris, Mandy, Kacy, Jennifer, Sara, and Candy. Meanwhile, Sister Ruth secretly tends to Sister Francis, Father Peter's wife who is actually the werewolf, as she undergoes an experimental blood treatment on a hospital bed hidden in the basement.

Robbie finds Alissa buying a gun from her old criminal cohort Lou Boy at The Penny Whistle. Robbie intervenes when Lou Boy gets physical with Alissa. Robbie compels Alissa to come with him after beating up Lou Boy and his cronies in a bar fight.

Robbie asks Alissa about Karla. Alissa tells Robbie that a werewolf killed her. Alissa explains she bought a gun with silver bullets with the intention of returning to Saint Matthias to kill the creature. Alissa adds that Father Peter and the two nuns are part of the conspiracy that results in at least one woman disappearing each month.

As the werewolf, Sister Francis kills Nikki and Iris in separate incidents.

Robbie returns Alissa to Saint Matthias just as the nightly lockdown begins. Sister Francis becomes the werewolf and kills Mandy, Kacy, Jennifer, Sara, and Father Michael.

To stop the detective from killing his wife, Father Peter beats Robbie to death. Before dying, Robbie manages to wound the priest with gunfire.

Alissa finds Father Peter. Peter reveals that a werewolf bit Sister Francis ten years earlier while they were in Brazil to visit Sister Ruth as part of their honeymoon. Peter and Ruth hoped they could cure Francis, but her hunger grew too difficult to control, so they fed her undesirables from their rehabilitation program. Alissa shoots Father Peter dead.

As the werewolf, Sister Francis kills Sister Ruth before charging toward Alissa. Alissa shoots the werewolf with silver bullets. Sister Francis reverts to her human form as she drops dead. Alissa and Candy escape outside to call the police.