Deadly Blessing (Wes Craven, 1981)

In a backward religious community called "Hitites" that lives in the Eighteenth Century, the pregnant Martha is happily married with the farmer Jim Schmidt, who is a former Hitite. Their non-Hitite neighbors are Louisa Stohler and her daughter Faith that hate the religious community ruled by Jim's father, the austere and fanatic leader Isaiah Schmidt. When Jim sees a mysterious shadow in his barn, he dies in a strange accident with his tractor. After his funeral, Martha welcomes her friends from LA Lana Marcus and Vicky Anderson that decide to spend a couple of days with her. When William Gluntz disappears stabbed by a shadow, his father and Isaiah come to Martha's farm looking for William. Then Isaiah makes an offer to buy the farm from Martha that says no and he calls her incubus. From this moment on, weird things happen in the community, Martha and her friends and Isaiah insists to blame the incubus.