For reasons known only to himself, the King of the Silver River has charged young Penderrin Ohmsford, barely more than a boy, with the daunting task of rescuing his aunt, Grianne, Ard Rhys of the Druid order, from her forced exile in the terrifying dimension of all things damned: the Forbidding. With the noble dwarf Tagwen and the prodigal elven princess Khyber Elessedil by his side, and with the outcome of the bloody war between the Federation and the Free-born at stake, Pen has accepted his mission without question. But not without risk, or sacrifice.

Shadea a'Ru, the ruthless Druid responsible for imprisoning the true Ard Rhys and usurping leadership at Paranor, has sent her agents and assassins in relentless pursuit of Pen and his comrades. In securing the talisman he needs to breach the Forbidding, Pen has paid a devastating price. Now if the Free-born forces, already decimated by the Federation's death-dealing new weapon, should fall, Shadea's domination of the Four Lands will be assured. Nothing short of Pen's success can turn the tide.

But Pen's challenge grows greater when he learns that his parents, Bek Ohmsford and Rue Meridian, have fallen into Shadea's hands. He must try to help them, but once within the walls of Druid's Keep, where Shadea's minions and dark magic lurk at every turn, Pen's survival is far from assured. Yet it will all pale in comparison to the horrors that wait inside the Forbidding, horrors poised to break free upon the Four Lands when the time is right.