Erika Magnus is a 14-year-old stirrer with complete confidence that she alone knows best. So, when her homesick sister Sif longs to return home to the island of Rongo, Erika successfully plots to get her there, and runs away to join her shortly after. Arriving on the island she finds the locals frightened by the changes happening to their world, and the cracks beginning to form in their once-perfect environment.
However, it isn't only Erika's home that needs her attention, Sif has caught the eye of Henry Jacka, a young American shell-collector, and Erika decides that won't do at all. But Henry has already guessed the secret of Sif's and Erika's family. He can hardly believe his eyes. He can hardly believe his own scientific conclusion.