More than a thousand years ago, the armies of the Arcosian Empire, led by sorcerer Mornhavon the Black, crossed the great sea and tried to conquer the land of Sacoridia using terrible dark magic. Eventually, Mornhavon was captured, and his evil spirit imprisoned in Blackveil Forest.

Since that day, the perimeter of Blackveil--now a dark and twisted land--has been protected by the magical D'Yer Wall. But in the centuries since the war's end, knowledge of the working of magic disappeared from Sacoridia, due to the fear and prejudice of a people traumatized by Mornhavon's sorceries.

Karigan G'ladheon is now a seasoned Green Rider--a member of the magical messenger corps of the king. But during her first year as a Rider, a rogue magician cracked the mighty D'Yer Wall. The spirit of Mornhavon, sensing the weakness, began to wake, seeking vengeance, and causing frightening aberrations throughout the land.

Karigan managed to transport the spirit of Mornhavon into the future, buying valuable time for her king and country. But how far in the future is Mornhavon now? A hundred years? Ten? Only one year? There is no way to tell.

And though Karigan and her fellow Riders have scoured the land searching for lost magical knowledge, and members of Clan D'Yer are camped at the wall, hoping to uncover its lost secrets, they were unaware of a threat to their kingdom that lay far closer.

For there were Arcosian soldiers who survived the Long War, and the descendants of those ancient enemies spent generations honing their powers of dark magic--a force against which the Sacoridians have no defense....