When a magical train called the Impossible Postal Express bursts through her living room floor, eleven-year-old Suzy Smith is thrust into an extraordinary adventure. She becomes a 'Postie' delivering packages across impossible realms like the land of the dead, the underwater kingdom of the mermaids, and the cloud-top home of the weather gods. Suzy soon discovers she's carrying a mysterious snow globe that could save or destroy the entire Union of Impossible Places, forcing her to question what's right and wrong in a world where rules are constantly rewritten. This thrilling adventure combines physics, magic, and heart as Suzy learns that impossible is just another kind of possible.