A newly released trailer for “Gwen” starts with a heartfelt prayer and ends with sobbing and shrieking. A nightmarish situation unfolds in between.

Set in in 1855 in Snowdonia, “Gwen” centers on a family in crisis. When Gwen (Eleanor Worthington-Cox, “Britannia”), her younger sister (Jodie Innes) and their mother (Maxine Peake, “The Bisexual”) aren’t praying for her father’s safe return from war, they are taking care of their farm and fighting the advances of a mining company determined to take over their land.

As if that wasn’t enough for Gwen to contend with, she’s convinced she hears someone outside in the fields at night and her mom’s behavior is becoming increasingly erratic. She walks in on her mother participating in some sort of bloodletting ritual. “As the blood passes from the body, so does the evil,” a voiceover explains.

Gwen just wants her mom to “be well again” — but it looks like her prayers won’t be answered.

You can catch “Gwen” in theaters and on VOD August 16.