The book takes place aboard a transoceanic luxury passenger airship, the Aurora, and is told from the perspective of its cabin boy, Matt Cruse.

Fourteen-year-old Matt Cruse is a cabin boy for the Aurora, an airship that stays afloat using a gas called "hydrium".

One year later, the now-fifteen Matt leaves his home in Lionsgate City, a fictionalized Vancouver, to accompany the Aurora on its voyage to Sydney, Australia.

Despite loving his mother and sisters dearly, Matt is relieved to be in the air where he feels closest to his father—a former sailmaker who died in an accident aboard the Aurora.

Matt is disappointed to learn that the Junior Sailmaker position he was promised has been given to the airship fleet's heir, Bruce Lunardi.

One day into the voyage, an ornithopter delivers two passengers to the ship: Kate de Vries and her chaperone Marjorie Simpkins.

They use Kate's harem pants as a balloon to lift themselves to ground level as Szpirglas' crew sets out to silence the passengers of the Aurora.

After tending to Bruce's wounds in the infirmary, Matt brings a sleeping elixir to the cook so that it can be added to the pirates' soup.

Szpirglas' crew murders Bruce in the engine room and chases Matt onto the hull of the Aurora in the open air.