Emily, Navin, and their crew of resistance fighters charter an airship and set off in search of Cielis, a mythical city believed to be located on an island high above the clouds. The mysterious Leon Redbeard is their guide, and there's a surprising new addition to the crew: the Elf King's son, Trellis.

Emily, Navin, and the crew arrive in the lost city of Cielis, but they soon realize it's not the utopia they expected to find. While Trellis and Luger are taken prisoner, Emily is forced to fight for her life in a series of tests that will determine who among the new generation of young Stonekeepers will join the Guardian Council.

Emily survived the chaos of the Guardian Academy, but Max Griffin has stolen the Mother Stone. Emily and her friends lead the Cielis Guard in a fight to stop him, but Max stands in their way. Emily seeks information from the Voice of her Amulet, but instead she discovers the Voice is much more sinister than she ever could have imagined.

Kazu Kibuishi's #1 NEW YORK TIMES bestselling series continues
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.

Emily, Trellis, and Vigo visit Algos Island, where they can access and enter lost memories. They're hoping to uncover the events of Trellis's mysterious childhood -- knowledge they can use against the Elf King. What they discover is a dark secret that changes everything. Meanwhile, the Voice of Emily's Amulet is getting stronger, and threatens to overtake her completely.