SYNOPSIS
Act I
Margared, the daughter of the King of Ys, is engaged to Prince Karnac, once an enemy of the city. During the engagement, she has admitted to her sister Rozenn that her heart belongs to someone else. Rozenn believes that her sister's beloved is a companion of their childhood friend Mylio, but Margared loves Mylio himself. The wedding ceremony begins. Mylio returns unexpectedly. Learning of his arrival, Margared calls off the wedding. Karnac curses the city and threatens to punish its citizens.
Act II
Karnac lays siege to the city. Margared learns that Mylio and Rozenn love one another and that the King agrees to their marriage. In triumph, Mylio returns to the city having defeated Karnac. Margared is filled with jealousy. Seeing Karnac, she suggests uniting to fight against the citizens. She promises to give him the keys of the floodgate that protects the city from high waters. The statue of St Corentin calls on her to repent, but she pays no heed to its request.
Act III
Mylio and Rozenn are celebrating their wedding. Margared and Karnac depart for the floodgate, but on the way she is overcome with doubts. Karnac reminds the girl of Rozenn and Mylio's happiness, and she is again seized with jealousy and the desire for revenge. Margared shows Karnac the way to the floodgate, which he opens. The waves of the sea begin to flood Ys. Margared appears at the wedding ceremony and declares that the city is doomed. Mylio kills Karnac. In horror, Margared understands what she has done and decides to pay for her actions by killing herself. She throws herself into the sea from a high cliff. Rozenn and Mylio follow her, but their path is barred by St Corentin. He orders the waves to abate and saves the city.
