Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition
Hi, I'm Matt, I'll be your Hero Today
We're introduced to Matt, the intrepid cabin boy, when he's asked to do a daring mid-air rescue of an elderly gentleman in a hot-air balloon (whom we later discover is/was Kate's grandfather). Our protagonist is revealed to be an honest, hard-working boy whose family fell on hard times after the tragic death of his father aboard the very airship he calls home. Unfortunately, Matt is passed over for a coveted promotion due to factors that are out of his control, and the unfairness of the situation has us rooting for him from the get-go.
Rising Action
Fasten Your Seatbelts—It's Going to be a Bumpy Ride
There's a lot of rising action in this book: Kate's exciting entrance; everyone surviving a terrifying raid by the pirates only to crash-land on said pirates' island; Kate and Matt's discovery of the cloud cat's skeleton (and then a living specimen); and then just when they think things are hunky-dory a devastating storm seemingly wrecks the Aurora for good. All of these problems build until we fall off our seats trying to see what happens next.
Climax
May the Force Be With You Two
Matt and Kate have found themselves captive—and a little drunk—in the pirates' base camp. Plus Bruce is off in the woods, wounded and bleeding, and the Aurora is just barely air-worthy and at imminent risk of being discovered by the pirates. Things are not looking too good for anyone except the bad guys. But, from the depths of a hydrium-filled cave, a flash of brilliance in the form of Matt Cruse emerges. He and Kate escape and go on to try and rescue everyone on board the Aurora—and for once luck might be on their side.
Falling Action
Mano a Mano
So it's come down to this: Matt versus Szpirglas, tussling on top of Matt's precious airship. The lesser pirates have mostly been defeated, so it's just the two of them left to hash out the Aurora's fate. The cloud cat throws a minor wrench in the situation by showing up and putting Matt between a rock and a hard place, but Matt ultimately reigns triumphant (with a little help from cloud cat's flock).
Resolution
One Big, Happy Ending
Things couldn't have turned out any better: Kate is famous for discovering a whole new species, and because of her newfound fame she gets to go to University. Matt saved the day and gets a ton of reward money for helping capture the pirates, so he gets to go to the Airship Academy to further his career on the Aurora. The ship has been fully repaired, and his family is taken care of back home. Oppel really ties it up in a neat little bow for us—everyone gets their happy ending. Well, except for Bruce.
Womp womp.