Black Christmas

William Edward "Billy" Lenz, a boy born with severe jaundice, is constantly abused by his hateful mother, Constance Lenz. With the help of her lover; Constance murders Billy's father, Frank on Christmas Eve 1975 and buries his body in the house's crawlspace. To prevent Billy from talking, she imprisons him in the attic. Years later, Constance attempts to conceive another child, but realizes that her boyfriend is impotent. She goes to the attic and rapes twelve-year-old Billy. Nine months later, Constance gives birth to their daughter, Agnes. Read more on Wikipedia.