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'. And the Groundlings are getting ready to defend themselves.
Above the clouds, Mr Mordadson is dispatched to Redspire, the heart of the piracy, to solve the problems however necessary and put an end to the piracy . . . and taking the armed Airship Cerulean - with Az Gabrielson as Captain - with him. 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.
. . . and 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 . . .