Doctor Faust is in his laboratory. While he asks himself about the vanity of his researches, from the outside he can hear chants yearning for spring and resurrection to arrive. But Faust is stubborn on taking his own life and in a blasphemus impulse, he invokes the devil. Mephistopheles arrives and offers him eternal youth in exchange for his soul. He persuades him by showing him the beautiful image of Margherita. The old doctor decides to sign the pact and he is suddenly turned into a young and elegant man, ready to embrace the pleasures of life.
Valentino, ready to leave for war, gives custody of Margherita, his sister, to his friends Siebel and Wagner, for them to look after while he is away. Mephistopheles arrives singing a song, then he predicts the future: he says to Wagner and Valentino they are going to die at war. To Siebel he says he will not be able to touch flowers without them drying up. Then he asks for a toast in honour of Margherita. Valentino is furious, he goes for his sword but this breaks in half. Aware of the satanic spell, he shoos the devil with the two halves of the sword made into the shape of a cross. Mephistopheles leaves and meets Faust, who is asking to meet Margherita. Faust sees the girl coming out from the church and while Mephistopheles gets rid of Siebel, he approaches her. Margherita kindly rejects him and Mephistopheles promises his help to the loving Faust.
In the garden behind Margherita's house, Siebel is picking flowers but when he touches them, they dry up. So he dips his hand in holy water and the spell vanishes, allowing him to place flowers on the house doorstep. Mephistopheles and Faust arrive. Faust is enchanted from the place and wants to leave but Mephistopheles calls him up and places a box with jewellery next to Siebel's flowers. Margherita, still enchanted by the monring encounter with the young doctor, sits at the spinning wheel and sings the Ballad of the King in Thule. When she sees the flowers and the box, she can't help putting the jewellery on. Old Marta comes in and she praises what look like gifts from a rich lover. Mephistopheles and Faust arrive. The devil predicts to Marta the death of her husband and starts courting her. The old woman is soon comforted from the bad prediction and takes a walk with Mephistopheles. Faust has the opportunity to court Margherita who accepts his advances but when he becomes too demanding, she runs home. Faust is content with the encounter and is convinced by Mephistopheles to stay and listen to what Margherita will say to the stars. The girl appears at the window and, thinking she is alone, declares her love for Faust, who, overwhelmed by passion, shows himself to the girl. Margherita indulges herself in Faust's arms while Mephistopheles laughs.
Seduced and abandoned by Faust, Margherita is mocked by everyone. Only Siebel is near by her side. Looking for God's comfort, she enters the church but she is tormented by Mephistopheles who reminds her of the past and predicts her damnation. The soldiers are back from war and among them there's Valentino, who understands what has happened. Faust and Mephistopheles arrive. The doctor wants to see Margherita again and the devil sings an offensive serenade to attract her to the window. Valentino is furious, he challenges Faust to a duel but it is not a fair battle because the doctor, helped by Mephistopheles, hurts Valentino who falls dying on the ground. Faust and Mephistopheles run away. Marta, Margherita and a group of people arrive. Before he dies, Valentino curses the sister.
It's Walpurgis night. Mephistopheles brings Faust in his sinister domain, the Harz Mountains. At a gesture from Mephistopheles, everything turns into a marvellous castle: queens and courtesans offer themselves to Faust to smooth the memory of the past. When the image of Margherita appears, with her neck circled with blood, Faust is distraught and orders Mephistopheles to bring him to her. Margherita is in prison because she has killed the child she had from Faust in an act of desperation. She is going to be executed at dusk. Faust tries to convince her to flee but when Margherita feels Mephistopheles's presence, she invokes the heavenly powers, rejects Faust and falls dead on the ground. Mephistopheles shouts "Damned!", while a heavenly choir sings "Saved!" closing the opera with a praise for resurrection.