The Groundlings are under attack. Approaching in darkness in huge airships, Airborn pirates are raiding refineries and pillaging Groundling factories—taking by force the supplies which used
to be offered as a tribute to the winged "gods." Now the Groundlings are getting ready to defend themselves. Above the clouds, Mr. Mordadson is dispatched to the heart of the piracy to
solve the problems however necessary, and he is taking the armed Airship Cerulean with him—with Az Gabrielson as Captain. But even on the ship there is unrest. Flight Lieutenant
Wallimson hates Az and plots to do whatever he can to undermine the wingless boy—while on the ground, unrest at Redspire is the last thing on Cassie's mind. The family business has been
destroyed by contact with the Airborn, and they scrape a precarious living taking Airborn tourists on tours. But as trouble is stirred up between the Groundlings and Airborn things go from
bad to worse for Cassie. And then her father goes missing.