Translator Noel Evans responds to an advertisement posted by John Canby and visits the man's home. Canby's companion, Fern, escorts, Noel to Canby's study. Canby translates Noel's name into numbers using numerology and informs him that his number is four, a sign of poverty. Noel assumes that Canby isn't interested in hiring him, but Canby asks him to look at an ancient tome and identify it. Noel reads the writing and informs Canby that it's 15th century Samarkind and he can translate it given time and resources. Canby agrees and tells him that he must move in and do it in the house, and will pay $750 for Noel's services. As Noel tries to argue, Canby hears a shuffling noise outside the door that Noel doesn't seem to hear. Canby goes to the door and looks out into the hallway but doesn't see anything.
When Canby returns to the room, he tells Noel that he's to start the translation immediately. Noel looks at the occult symbols in the room and informs Canby that he has no interest in the supernatural. Canby doesn't care and assumes that Noel has accepted the job. He pays him one month in advance and explains that his twin brother lived and worked in the manor until he died. Fern comes in and tells Noel that he can find his way to his bedroom. After Noel leaves, Fern suggests that Canby shouldn't have the book translated. However, Canby insists that he must know what it reads and embraces Fern.
Later, Fern goes to find Noel and tells him that Canby wants him to go to work. He asks if he's the first translator that Canby has hired, and Fern informs him that there were two others, but they both quit. As she goes, Noel asks if he can trust her and Fern assures him that he can.
As Noel works on the translation, Canby informs him that it has precedents in the works of the Necronomicon. He tells Noel that some of the passages were never translated. When Noel asks why they left, Canby says that they found one passageway that they refused to translate. Canby then hears the same shuffling sound as before from outside the room. He checks and confirms that there is nothing there, and tells admits to Noel that the other two translators left out of fear of what they found in the book. He avoids any further questions and invites Noel to join him for dinner.
At dinner, Noel is seated with Canby, Fern, and a goat. Canby claims that the goat, The Falling Tower, is his father. The talk turns to Fern's position in the house and Canby explains that she is indispensible. Fern says that in witchcraft, women dominate the men. Canby hears the shuffling noise again and Fern dismisses them as rats, but Canby doesn't believe her. They discuss the rise of witchcraft and the Black Mass in medieval times, and Fern speaks of it as if she were there. Noel finally wonders if the distracted Canby is expecting someone, but Fern ignores Canby's concerns, picks up a toad from the table, and asks it to kiss her.
Later, Noel finishes translating the book and tells Canby and Fern that he understands why the other two translators left. He gives Canby his money back and prepares to leave, and Canby draws a gun and orders him to read. Noel informs him that the passageway speaks of how a sorcerer can resurrect himself and then complete the tasks that he left unfinished in his life. A particularly powerful sorcerer can reanimate himself even if dismembered, but he can only harm those who believe in his power. Noel concludes by informing Fern and Canby that the passage contains a curse, and that whoever reveals its secrets is doomed to be flayed over burning coals and himself dismembered.
Shocked, Canby goes into a trance and Fern leaves him, gesturing Noel to follow him. Outside in the hallway, Fern explains that Canby murdered and then dismembered his brother, kept the head, and buried the other pieces outside in the garden. When Noel demands answers, Fern informs him that they will be holding a Black Mass and she hopes to see him there. She tries to kiss him, forgetting that she's holding the toad, but she continues. Canby comes out, dressed for the Black Mass, and tells Noel at gunpoint that he has to finish the translation.
As Noel works to complete the transaction, Canby conducts a series of rites to protect the study from Satanic influences. He hears the shuffling noises again and Noel hears them as well, and Canby says that it's rats. Noel throws open the door and finds a disembodied hand and foot crawling toward the study. He slams the door shut and Canby explains that he killed his brother, a more powerful sorcerer, and then dismembered the body and kept the head in the study closet. There's a pounding sound from the closet, and Canby tells Noel that Fern conspired with his brother and took him as a lover to gain power over both of them.
When Fern arrives, Canby takes a sword and charges Fern, but she enchants and tells him to go to the chamber. Entranced, Canby goes there and Fern invites Noel to follow. In the room they discover that the closet door has shattered and Canby's brother has reassembled himself. The brother takes a sword and confronts his murderer, who is compelled to lie down at the altar and let himself be decapitated.
A minute later, Noel bursts into the chamber and finds the goat seated at Canby's desk. There is no sign of Canby or his brother. Fern comes out and explains that the brothers are reunited, and suggests that Noel come to her room. She kisses the translator and starts to go, expecting him to follow. As he does, Noel asks if there is anything to the curse about the reader being burned and dismembered, but Fern simply smiles and leads him away.