This is a riveting tale of two quests. In the first, Cara Diana Hunter searches for an ancient story that may unravel the secret of a long enmity between the unicorns and the monstrous delvers. In the second, Cara's father journeys to free her mother from the Rainbow Prison. As Cara travels through the strange and terrifying underground world of the delvers and to the court of the centaur king, her father travels from mysterious India to the depths of the Rainbow Prison itself. Who can be trusted? Who is the enemy? Readers will be at the edge of their seats with this multi-stranded story filled with wonder and suspense.