The maze-like castle of Southmarch stands sentry along the border between the human kingdoms and the land of the immortal Qua. Now, the darkness from beyond that border has begun to enfold Southmarch - or Shadowmarch - the Qua's ancient home. To stop the darkness falling, the Southmarch royal family must face their human enemies, supposed friends and the family curse. Twins Barrick and Briony shoulder impossible burdens as their father is imprisoned and their brother murdered. Briony flees towards her father and the slave armies of the Autarch, while her brother Barrick crosses the Shadowline gripped by madness ..

A year ago, the March Kingdoms were at peace, the Eddon family held the throne, and all was right in Southmarch Castle and the north of the world. Now the family has been shattered. King Olin Eddon is a prisoner in a faraway land. Olin's heir Kendrick is dead - slain by treachery and dark, bloody magic - and Kendric's younger brother and sister have barely escaped several attempts on their own lives. With their father and brother taken from them, the royal twins Barrick and Briony have done their best to hold the kingdom together, but now Barrick has been captured in a failed war against the immortal Twilight People and Briony has been forced to flee the castle. Everywhere in the north the fierce Twilight People, led by the ageless warrior-witch Yasammez, hold sway. Old magics are stirring beneath the ancient castle and behind the Shadowline, and the machinations of gods, fairies, and mortals threaten to spread devastation across the entire world. Meanwhile, the Autarch, the insane god-king of the southern continent, has set in motion his plan to bring the entire northern world - and most especially Southmarch Castle - under his way. Behind the Shadowline, Prince Barrick Eddon of Southmarch is lost and spellbound in the land of the fairies. Though he has barely begun to uncover the strange secrets of his own past, Barrick must also solve the mystery of his even stranger destiny - a destiny which will lead him to places no man has ever gone and force him to take on a burden even the greatest hero couldn't bear - preserving the lives of all humans and fairy-folk. As she flees Southmarch, Princess Briony finds both allies and deadly enemies in unexpected places far from the land of her birth. In her quest to survive and win back her family's throne she encounters spies and murderers, traveling players and ancient gods. During their desperate journeys the twins discover that even a land's rulers may know little of its true history, and that both families and nations can hide dark and terrible secrets. But even if Barrick and Briony survive learning the astonishing truths at the heart of their own family and of Southmarch itself, they must still find a way to do the impossible - they must reclaim their kingdom and rescue their home and people from a multitude of powerful enemies - from traitors, tyrants, a god-king, and even the angry gods themselves.

With King Olin imprisoned and Prince Kendrick slain, the royal twins Barrick and Briony have been forced to flee their homeland. But both families and nations can hide dark and terrible secrets. Even if Barrick and Briony survive learning the astonishing truths at the heart of their own family and of Southmarch itself, they must find a way to reclaim their kingdom and rescue their home-from traitors, tyrants, a god-king, and even the angry gods themselves.

The long-awaited concluding novel in Tad Williams' thrilling epic Shadowmarch series. Southmarch Castle is about to be caught between two implacable enemies, the ancient, immortal Qar and the insane god-king, the Autarch of Xis. Meanwhile, its two young defenders, Princess Briony and Prince Barrick, are both trapped far away from home and fighting for their lives. And now, something is awakening underneath Southmarch Castle, something powerful and terrible that the world has not seen for thousands of years. Can Barrick and Briony, along with a tiny handful of allies, ordinary and extraordinary, find a way to save their world and prevent the rise of a terrible new age-an age of unending darkness?