Readers who fell in love with Twig, Ben, and the fierce, wild unicorns of misty Lonehorn Island better get ready for an even more action-packed, heart-wrenching sequel. In the land of the unicorns a thief is at work. One so skilled and so bold, he's even taken the queen's prized unicorn. Now all of the captive unicorns are in danger and only Ben and Twig, the last unicorn riders, can save them.

Twig and Ben are unicorn riders—guardians whose job it is to keep the last free unicorn herd safe. But a new danger is threatening the beautiful, mysterious creatures of Lonehorn Island. A thief from Terracornus has snuck onto the misty island and stolen Ben's loyal unicorn, Indy. There's only one path for Ben and Twig—straight into the secret, shadowy heart of the island and through the passage to Terracornus.

But their rescue mission is unexpectedly complicated by a secret Ben has been hiding. A secret about the Queen of Terracornus who has enslaved all the unicorns of Ben's homeland. A secret that could save them all—or start a war.