The boys gain an unexpected addition to their workforce with the arrival of Pythagoras's feisty younger brother, Arcas. Charged with escorting a valuable cargo across the desert, the gang travels into the unknown with a ramshackle caravan of strangers.

It is not long before their journey takes a decidedly spooky turn; after spending a night in a temple dedicated to the Furies, it soon becomes clear that one amongst their number has something to hide. As danger closes in and a dark secret is exposed, our heroes are forced to confront some uncomfortable truths as they fight for their lives under the desert sun.