Kilmore Cove hides a traitor and Jason, Julia, Anita and Rick will end up looking for him in places unknown even to Ulysses Moore.

In Kilmore Cove there is a traitor, someone willing to do away with the Gates of Time and its guardians. So Jason, Anna, Rick and Julia's lives are in danger again... but this time they can't get rid of him without answering many riddles: who is their enemy, why does he want to destroy them, how can they stop him? Fortunately, there is a place where all the answers can be found: Agarthi, the legendary city of ice. Although no one, not even Ulysses Moore, has ever been able to find it ...