A lot has changed for Kate in a year. She and Tom are now full-fledged conductors of the steam-powered, animal-saving Great Secret Intercontinental Railway. Life is good!

Or good-ish, anyway. Her uncle Herbert has gone missing, and the worsening climate means that there are more and more animals that need help all the time. How many times does Kate have to save the world before it stays saved?

And her real life isn't exactly perfect either. She flunked her audition for the junior high musical and got stuck in the chorus, while her archenemy Jag got a lead.

So, out of desperation, Kate breaks the rules and takes the Silver Arrow out on an unsanctioned mission, to find Uncle Herbert and bring back balance to the world. But she quickly discovers she's not the only one on the Great Secret Intercontinental Railway. There's a mysterious train called the Golden Swift out there too, with an agenda of its own. Is it an ally? A rival? An enemy? A bit of all three?

The question will turn Kate's world upside down, take her from the Scottish Highlands to the Australian outback to the bottom of the Bering Sea, and lead her straight on a collision course with the mysterious masters of the Great Secret Intercontinental Railway itself. Because when you're a human being fighting to save nature, are you the hero or are you the villain? There are no simple answers.