Hazel receives a gift from her grandmother's jewelry collection. She appreciates its beauty but not its power, until she meets a sea creature whose kingdom is in danger of being wiped out. Kai rules a colony of Perlnauts, ancient lake dwellers who are in desperate need of the pearl jewelry used to sustain their underwater realm. He suspects the humans have stolen the jewelry, and he wants it back. With Kai's help, Hazel vows to solve a mystery that joins their worlds.