On May 18, 1980, eleven-year-old Jessie Marlowe and her best friends, Eddie and Sam, are in a forest near Mount St. Helens when the months of wondering whether the volcano will erupt are finally answered--all three are badly burned, but it is up to Jessie to protect the boys as best she can and hope that somebody comes to rescue them.

While their parents are away doing research, brothers Duffy and Sumo Pugg go with their cousin, Mister Come-and-Go, to Kokalaha Island, where they meet Aunt Lulu and become trapped in an erupting volcano.