Amy and Dan have managed to rescue one of the Cahills kidnapped by the Vespers, but the remaining hostages are still in peril. Their search for the next ransom item leads Amy and Dan to Turkey and then to Italy where a visit to the site of an ancient disaster changes everything. The Vespers are far more dangerous than the siblings ever imagined and, even worse, it looks like they have an undercover mole posing as a Cahill. Amy and Dan have to face the biggest decision of their lives with nowhere to turn... and no one to trust.