Sal, Joe, Francie and Humphrey misplace their famous mapmaker mother as they begin the Great Race to map a rail route through an uncharted wilderness. Their father didn’t return from his last expedition and now their money is gone. This race is their last chance. They have twenty-eight days to find and map the best route. There’ll be bears, bees, bats, river crossings, cliff falls, impossible weather—but worst of all, they’re racing five teams of adults who do not play by the rules.