The action takes place in the early 16th century in and around Cologne.
Ruprecht, a knight returning to Europe from America, stops over at a squalid tavern in a German settlement. From the next room the cries of a woman tormented by visions can be heard. Ruprecht comes to her assistance and she, unexpectedly calling the knight by name, tells him her story. Her name is Renata and in her childhood she began to see a fiery angel called Madiel, whom she came to love with all her heart. On growing up, Renata wished to be united with him in a physical sense, at which Madiel became incensed and disappeared, later appearing to her in the guise of Count Heinrich. The Count took the girl to his castle and they were happy, but one day Heinrich left without warning and never returned. For many days the abandoned Renata has sought her beloved, and at night she is pursued by evil spirits. The mistress of the tavern tells Ruprecht that her strange guest is rumoured to be a witch; she then brings in a fortune-teller who promises Renata a dreadful outcome.
Ruprecht accompanies Renata on her search for the Count: he is in love with Renata and swears to serve her faithfully; she, however, is immersed in a study of demonological treatises and can think only of how to reclaim Heinrich – Madiel. In the room where they have now taken up quarters mysterious noises can be made out – through these, the spirits relate that Heinrich will now enter the house, but no-one comes. The bookseller Jakob Glock arranges for Ruprecht to visit the famous sorcerer Agrippa von Nettesheim, from whom the knight attempts to learn the secrets of magic.
Outside Count Heinrich's house, Renata in vain begs to be admitted. Ruprecht returns from Agrippa. Renata demands that the knight challenges the Count who has insulted her to a duel and kill him. Upon seeing Heinrich on the balcony, the heroine again perceives him to be a fiery angel. During the duel, Ruprecht – whom Renata at the very last minute forbade to attack Heinrich – is seriously wounded. Raving, he imagines the laughter of the redskins against whom he fought in America.
As soon as Ruprecht's condition improves, Renata declares to him that their relationship cannot continue no longer and that she intends to shut herself away in a convent. Ruprecht goes to the tavern to drown his sorrows and meets Dr Faust and his friend Mephistopheles who are travelling across Europe and who invite the knight to join them on their journey.
The Inquisitor arrives at the convent to exorcise the demons: ever since Sister Renata came here, the nuns have been possessed by evil spirits. During the exorcism a Bacchanalia begins: some of the sisters call Renata a saint, while others almost rip the Inquisitor to shreds, declaring him to be a myrmidon of Hell. Mephistopheles brings Ruprecht to the convent and shows him what has happened to Renata. The Inquisitor condemns her to be burnt at the stake.