Neither Cory nor Thomas could imagine how a trip across the desert in a borroed 1992 Ford Explorer could end in a discovery that would rock the country. A broken drive shaft stranded them. The decision to hike home across sacred Indian lands took them to the glass canyon. The discovery of a wooden door in the wall of that canyon introduced them to a people who had hidden in the deep caves for a hundred and sixty years. The only possible danger would be to the people themselves. They would not be immune to diseases we take for granted. They would be confused by a civilization that passed them by. Their light-deprived skins would be easily burned by a sun they'd never seen. There shouldn't be any danger to the boys unless an old enemy sends an assassin to settle his vendetta with them. Such an assassin would be more devious and vicious than his master. The boys recognize him only after Salah, their mentor, is struck down in front of them. They have to dig deep for courage enough to survive and find justice for Salah and his family.