
In the legendary Breton city of Ys, the princess Margared is consumed by jealousy when her sister Rozenn marries the warrior Mylio, whom Margared also loves. In her fury, Margared conspires with the enemy prince Karnac to open the sea gates and flood the city. Overcome with remorse, Margared sacrifices herself by leaping into the waters to stop the deluge, and the city is saved.