Ian Wigby is about to find out that he is a very special boy. Along the southern coast of England, atop the White Cliffs of Dover, stands a castle. And at that castle’s old keep is an orphanage. Delphi Keep has seen many youngsters come and go through its gates, and Ian Wigby and his sister, Theodosia, are happy to call it home. Life has always been simple at the Keep, and the orphanage safe, until one day, Ian and Theo find a silver treasure box. And within the box, a prophesy. Three thousand years ago a great Greek oracle wrote of a quest. A quest on which the fate of the world depends. A quest that names two children—Ian and Theodosia. Suddenly Delphi Keep is no longer safe. And Ian and Theo, along with a very special group of friends, realize they must unravel the meaning behind the scroll of Dover cavern before darkness falls on the world. And before an unfathomable evil catches up with them. From the Hardcover edition.

Since Ian Wigby and his sister, Theodosia, found the silver treasure box and the prophecy within it, their world has changed. There's no denying what they discovered in Morocco: a powerful evil is budding, and to defeat it, and save the world from darkness, six uniquely gifted children must be gathered. According to prophecy, a trip through the magical portal near the castle will bring them to the third Oracle—a child with extraordinary powers to heal. But the very same prophecy foretells Ian's death should he venture through the portal again. Everyone agrees: to risk Ian's life is too great a gamble. But when a terrible curse enters the keep, it becomes clear that there is no other choice. If Ian and Theo stay in Dover, all will surely be lost, but to follow the prophecy, they will risk their lives and everything they have ever held dear.

Delphi Keep is awash in activity, and for Ian, Theo, and Carl, their safe haven might be nearing its end. The Royal Navy has taken the keep to use as a hospital and the tunnels running under the keep and the castle are ideal to set up a central communications outpost for the approaching war. The earl is happy to help the effort, but now the keep is no longer safe for the orphans and they must be evacuated to his winter residence. Ian, Theo, and Carl know that if they're sent away, they'll no longer be protected. But more important than their safety is deciphering the third prophecy. All clues point to a quest. The orphans don't know where they must go, but they know they must rescue the Secret Keeper. To do that, however, they need to work out who this Secret Keeper is. And what, exactly are the secrets he's keeping?