Cronus feared an old curse: one day a son would take his throne. To stop it, he did something terrible — but Rhea hid little Zeus away, and from him came the greatest war the cosmos has ever seen.

When young King Arthur's sword breaks in battle, Merlin leads him to an enchanted lake. There, from waters as still as a mirror, the mysterious Lady of the Lake offers him Excalibur, the most famous sword in all of legend.

After twenty years of peace, Camelot stands at the height of its glory. But secrets are growing inside the castle, and Mordred's ambition waits quietly for its moment. So begins the slow, sorrowful fall of the fairest kingdom that ever was.

On the plain of Camlann, two armies meet for the last battle. Arthur faces Mordred, Excalibur returns to the lake, and a boat crosses the mist toward Avalon. The end of the Arthurian legends — and the promise of the once and future king.