Saturday the 14th

The vampire Waldemar from Transylvania travels with his wife to Pennsylvania expecting to buy a derelict mansion, but the real estate agent Marge tells him that he needs to wait. Meanwhile, the owner "Uncle Henry" dies, and his Attorney reads his will, and the Hyatt family inherits the house. John Hyatt, his wife Mary, his teenage daughter Debbie and his ten-year-old son Billy move to the mansion eager to renovate to become their home. The children hate the place and Billy finds a book, "The Book of Evil", and leaf through. Meanwhile, John finds a note from Uncle Henry in the refrigerator saying that "The Book of Evil" shall not be opened; otherwise, evil will be released, and the world will be destroyed. Soon the house is infested by monsters that kill Marge and the next-door neighbor, but John does not see them. When Mary finds that the attic is crowded of bats, John calls an exterminator and Van Helsing. John intends to call over the party he will give to family and friends to show the house, but Van Helsing tells him to keep the party.