Volume III, Chapter 5 represents the resolution of this complex, gothic novel, which titilated its audience and is so famous for shaping the gothic genre. In this section of the novel, Ambrosio and Matilda are taken in front of the Inquisition. Because they declare they are innocent, they are both tortured, until Matilda finally declares her guilt and then she is sentenced to be burned to death. Ambrosio however maintains his innocence. Whilst he is awaiting his second bout of torture, Matilda comes to him in a vision and urges him to sacrifice himself ot Satan, just as she decided to do, telling Ambrosio to sell his soul and therefore escape more torture:
Let us for awhile fly from divine vengeance. Be advised by me; Purchase by one moment's courage the bliss of years; Enjoy the present, and forget that a future lags behind.
She leaves behind the mystic tome that allows him to perform the ceremony of giving his soul to Satan. Ambrosio confesses his guilt when faced with the instruments of torture of the Inquisition. He is told he will burn too. However, at this moment, he summons Lucifer, who tells him his life can be saved, but only for the price of his soul. Ambrosio hopes for God's pardon, but eventually, after being told that this does not exist, he signs the contract and is removed from his prison and taken to a barren plain.
Here, Lucifer tells Ambrosio that Elvira was his mother, which makes Antonia his sister, making his sins even worse, as he committed incest as well. Lucifer reveals it was his plan to gain Ambrosio's soul, and he used Matilda to help him gain his objective. Ambrosio is then dropped on the rocks below and is tortured for six days before dying and being damned forever.