As the new Keepers of the School, sixth-graders Ben and Jill must decipher a handful of clues written as maritime riddles to save their school from demolition by a greedy company.
Ten-year-old Flavia and her friends encounter the Roman admiral Pliny before making a journey to her uncle's farm near Mt. Vesuvius, where they try to solve a riddle, reunite a family, and get out of the path of a natural disaster.