Airborn by Kenneth Oppel

Imagine a world which is almost like ours. Airplanes do not exist. Instead, people travel in leisurely luxury to their destinations on huge airships. Matt Cruse is a cabin boy on one of these magnificent airships named the Aurora.

One night, when Matt is on watch in the Aurora's crow's nest, he and the crew rescue a balloonist, who dies, leaving behind a puzzling journal filled with drawings and detailed descriptions of a strange, never-before-discovered flying animal. Much to Matt's surprise, on their next voyage out, one of the passengers, young Kate de Vries, turns out to be the grand-daughter of the dead balloonist. She is intent on proving the truth of her grandfather's story of the strange new animal, even though her parents and scientists think her grandfather was hallucinating when he wrote of his find.

Kate enlists Matt in her quest for evidence that will prove her grandfather right. Along the way, they battle Kate's domineering but dim-witted chaperone and crafty and evil pirates.

The author takes you from one edge-of-your-seat, hold-your-breath adventure to the next in this strange and beautiful parallel world.