Shortlisted for the Waterstones Children's Book Prize 2019.

"Great fun!" - Philip Reeve, author of Mortal Engines

"Rip-roaring inventive adventure" - The Independent

When Suzy hears a strange noise in the middle of the night, she creeps downstairs to find a train roaring through her house. But this is no ordinary train. This is the magical delivery express for the Union of Impossible Places.

Whisked on board by a troll-boy, Suzy's world is turned upside down when she's asked to deliver a cursed package to a fearsome sorceress. And quite suddenly, Suzy realizes the fate of the Impossible Places is in her hands...

Suzy can't wait to return to the Union of Impossible Places on the Impossible Postal Express. But when she arrives, she overhears a dastardly plan to destroy Trollville from a shadowy and unexpected villain. Suzy and her friends must race from magical cloud-worlds to secret caverns to catch the culprit, before Trollville comes crashing down...