Navin and his classmates journey to Lucien, a city ravaged by war and plagued by mysterious creatures, where they search for a beacon essential to their fight against the Elf King. Meanwhile, Emily heads back into the Void with Max, one of the Elf King's loyal followers, where she learns his darkest secrets. The stakes, for both Emily and Navin, are higher than ever.

After tragedy strikes their family, Emily and Navin move with their mother into the old, mysterious home of their great-grandfather. On their first night in the strange house, Emily and Navin's mom is kidnapped by a tentacled creature. Determined to rescue her, Emily and Navin are led into a world of robots, talking animals, flying ships, new friends... and enemies. Emily learns that she is a Stonekeeper and essential to the survival of this world, and that her incredible story is only just beginning.