Eleven-year-old Suzy Smith knows exactly how the world works. Thats science, and Suzys good at science. But when she wakes in the middle of the night to find a troll building train tracks through her living room, defying all the laws of space and physics, Suzys world is turned upside down. How is any of this possible? As the trolls explain, its fuzzics, which is like physics only fuzzier! Well Suzy has no choice but to sneak on board and wrangle herself a position on the Impossible Postal service, a train that delivers to impossible placeseverywhere from ocean-bottom shipwrecks to Trollville to space! Then, on Suzys very first deliveryto the evil Lady Crepuscula of the Obsidian towerthe package itself begs not to be delivered. A talking snow globe claiming to be a prince, Frederick promises that the fate of the entire Union of Impossible Places now rests on Suzys shoulders. But protecting Frederick may mean lying to and even endangering her friend and colleague, the postmaster Wilmot. Can Suzy save her friends and the entire Union of Impossible Placesall while upholding her duties as deputy postmaster?