The story is based on a medieval legend and revolves around Esclarmonde, an empress and sorceress of Byzantium. Sequestered by her emperor father, Phorcas, who has recently abdicated the throne to her, she bemoans her love for Roland, a knight and Count of Blois, believing she will never be allowed to be with him. Following a suggestion from her sister, Parséïs, Esclarmonde uses her magic powers to transfer Roland to the magic island where she joins him and continues to do so on a nightly basis and, hiding behind a veil, never reveals her identity. She reveals to him also that his country is in danger, attacked and besieged by the Saracens, and grants him a magic sword with which he will be capable of defeating the enemy. It will serve him well as long as he will remain faithful to her.