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.