With Marco gone and the first Loculus lost, Jack, Cass, and Ally are no closer to saving themselves (or the world) than when they first arrived at the Karai Institute. But when Bhegad tracks down Marco deep in the desert, the kids are off on the next leg of their quest—to the ancient city of Babylon. There the kids find themselves faced with a daunting choice that makes them question everything they've learned so far. It's a gut wrenching decision, but what the kids don't realize is that it's also a trap. Surprises pile on surprises until a long-lost figure from Jack's past returns, and the kids find themselves forced to engineer an escape that might just turn out to be a different kind of trap altogether....