In this follow-up to the internationally successful The Mapmakers' Race, the Santander children are drawn into a community’s rebellion against a despot and use their mapping skills to avert an environmental scam.

Sal, Joe, Francie and Humphrey Santander are mapmakers looking for their father, a famous explorer who disappeared on his last expedition. Their search takes them to Cruxcia, where the people are fighting to protect their land from the all-powerful Grania Trading Company. The Santanders’ mapping skills may be the missing piece in the Cruxcian race to save the ancient valley—and the key to reuniting their family.