An all-American family inherits a deceased uncle's house. John (Richard Benjamin) and Mary (Paula Prentiss), together with daughter Debbie (Kari Michaelsen) and son Billy (Kevin Brando), move in, but Waldemar (Jeffrey Tambor), a vampire, and Yolanda (Nancy Lee Andrews), his wife, want desperately to get into the rundown house because it contains a book of evil.
Billy finds the mysterious book. He reads of a curse hanging over the date of Saturday the 14th. As he turns the page, a monster is unleashed, and with each turn another disappears from the page and is materialized within or outside the home. The house is soon swarming with monsters.
Strange things start happening: eyes appear in John's coffee, sandwiches are mysteriously eaten, the television tunes into The Twilight Zone only, dirt is found in Mary's bed, dishes get done by themselves, neighbors disappear. As this is happening, neither John or Mary suspect anything, oblivious to the spooky occurrences around them.
Waldemar gets into the house by turning into a bat. Mary keeps hearing noises at night which she thinks are made by owls, but are actually the sounds of Waldemar the bat. John hires an exterminator to get rid of the owls. The exterminator turns out to be Van Helsing (Severn Darden), who is also after the book of evil.
John and Mary begin planning a housewarming party for Saturday the 14th. Guests arrive but cannot leave. When they try, a thunderstorm appears outside the door. As the night unfolds, the monsters begin to kill the guests one by one.
Eventually a duel between Van Helsing and Waldemar and Yolanda erupts, where it is discovered that Helsing wants the book in order to rule the world, and Waldemar and Yolanda were only trying to stop him from getting his hands on it. Good triumphs over evil, as Van Helsing and the monsters are defeated.
The family ends up in an upscale new home while Waldemar and Yolanda keep the original house as their own.
What does Waldemar and Yolanda want that is in the house?
book of evil