The adventure begins with Tintin on the train reading how the Sanders-Hardiman Ethnographic Expedition has returned from a trip to Peru and Bolivia. The gentleman reading over Tintin's shoulder predicts trouble, drawing a parallel between what happened with the curse of King Tut-Ankh-Amen's tomb and these explorers violating the Inca's burial chambers. "What'd we say if the Egyptians or the Peruvians came over here and started digging up our kings?" asks the gentleman; "What'd we say then, eh?" The comment is important, not only because tragedy does strike the seven members of the expedition as they fall prey to the Crystal Balls of the book's title, but because one of the themes that Hergé develops in this particular epic is the respect Europeans should have for other cultures and ways of life.