Mac Stuart (Robert Elston), a professor of psychology at a small mid-western college, has introduced a course in Superstition Throughout History. At a party he gives for his students, Jill (Anitra Walsh) arrives with the Red Book of Appen, an old book of spells and enchantments which she found while collecting for a charity book fair. The students light-heartedly decide to conduct one of the rituals, Enchauntment for the Summoning for the of Wytches.Jill conducts the ritual but at the end nothing happens and the party mood resumes. No one notices the strange change in Jill, who stares about the room as if she's never seen it before. On the way home, Jill's boyfriend Alan (Darryl Wells) is puzzled by her strange behavior but leaves her at the door promising to pick her up for class tomorrow.Later at Mac's house, he is surprised at the reappearance of Jill. She tells him that she is Margery of Jouremain, who was hanged as a witch in 1648. At first Mac thinks it's all a joke, but she proves herself by viciously killing his dog and showing a birthmark on her wrist, identical to one on Mac's wrist, which according to the book is the Mark of the Witch.The next morning Alan accuses Mac of seducing Jill. Mac tells of the evening events and the two understand that in order to save Jill they must go along with the spirit that is in her and try to catch the witch off guard, thereby freeing Jill's body from the spirit.In the following days Alan and Mac desperately search through the Red Book for a clue that will free Jill. The witch begins to kill all those who harassed her at the party: Harry, his girlfriend Sharon, and others in a bloody ritual in the woods. Realizing they must stop her, Alan and Mac exhaust every source on the subject and finally, through the powers of his own mark, Mac finds a hidden clue: "Shadows upon shadows encircle the unholie one with the sign of the holie."The witch decides that Alan and Mac are getting too close to stopping her and she arranges another ritual to kill them. In a life or death struggle, Mac forces the witch's eyes open while Alan rushes to get a crucifix. He gives it to Mac who presses it against the witch's chest. With a horrifying scream, the bloody and bruised witch reaches out to Mac. Mac intuitively knows that her kiss will mean his death, but he cannot resist. They kiss and spin away into nothingness. Jill is freed and Alan is left to explain.