At long last, Matt Cruse is at the helm. Though it's only a summer job piloting a humble aerocrane, he's thrilled to be a small part of something big. With every load, he's helping to build the Celestial Tower, Paris's extraordinary gateway to outer space. But Matt's idyllic summer is short-lived. He narrowly survives a deadly attack by the fanatical Babelites, who are opposed to humans reaching the heavens. Worse still, his nights spent stargazing with Kate de vries must end when she's summoned back to Lionsgate City by her parents. It's time she began to think about getting married.

But then a chance of a lifetime boosts Matt's hopes of being airborne once more. Canada wants to be the first nation to reach space, and the Minister of Air has asked Kate to join the initial expedition as an expert on aerial zoology. There's a place for Matt, too-if he can pass the gruelling tests to become an astralnaut on board the incredible ship Starclimber.

It's a race to the very top, and Matt is determined to be a part of the adventure. But can he outlast his competition? And if he is chosen to join the crew, will they ever return to earth?