In a terrifying and brutal future world, cities are mounted on giant wheels. They hunt each other to the death. Cataclysmic wars and stalking robotic hunters are revisited in a stunning relaunch of one of the greatest post-apocalyptic adventure series ever written. All four installments of Philip Reeve's internationally bestselling quartet are now available as a single ebook, featuring exclusive bonus material – the previously unpublished THE TRACTION CODEX.