An extensive episode of magic occurs in the fictional Life of St Andrew the Fool a work probably dated in the 10th century. A woman in Constantinople turns to the magician Vigrinos, a deceptively pious man, who cures her husband of his lust by seemingly harmless means: fighting an oil-lamp in front of her icons and tying four knots on a girdle. A series of impure dreams, however, of wild sexual desire, in which an Ethiopian, a black dog and the ancient statues of the hippodrome play a leading role, terrify the woman and make her realize that the devil himself has fallen in love with her. The outrageous results of Vigrinos’s magic are revealed to her after fasting and prayer: her icons, smeared with excrement, have lost divine grace, while the oil-lamp has become the vessel of an impure sacrifice to the demons. Terrified, the woman resorts to Epiphanios, the spiritual son of St Andrew the Fool, who comes to her assistance and remedies the situation. In turn, he becomes himself the target of demons in his dreams, and finally defeats them while asleep. As revealed in a further dream, the four knots of the girdle had bound a demon to the woman, and St Andrew explains to his pupil the means which the magicians deploy to deceive their victims regardless of how innocent their objective may seem, and make them vulnerable to the evil influence of demons. In accordance with the firm position of the Church which considers magic as demonic in all occasions -a position also introduced in secular legislation in the 10th century-, this episode offers the modern reader a glimpse of how magic functioned in practice, or, rather, of how a pious Byzantine thought it functioned. Operating under a Christian pretext, the magical act reverses and invalidates Christian ritual and symbolism and thus neutralizes their protection over the believer. In a deceptive world where nothing is what it seems, the real nature of the phenomena can only be detected through the dreams of the faithful and the intuition of the true saints, who are in turn difficult to be recognized. It is interesting to note the function of dreams and the appropriation of icons in magic -which can also be attested in other sources- as well as the role of women in a story, in which the boundaries between faith and credulity, religion and superstition are explored.