Tighe lives on the Worldwall. It towers above his village and falls away below it. It is vast and unforgiving and it is everything they know. Life is hard on the Worldwall, little more than a clinging on for dear life. And then one day Tighe falls off the world. And falls, and falls and falls ...and survives. He finds a new part of the Worldwall, a city, more people than he ever imagined existed and a war. A war fought by the Popes and their armies. A war Tighe must join, a war that will take him on a journey into the heart of the mystery behind the Worldwall. ON is a superbly confident novel of a changed world. It has echoes of a Canticle for Leibowitz and The Book of the New Sun. It is a remarkable feat of imagination and sustained narrative drive. Its hero is immensely appealing. Coming after SALT it is evidence of an extraordinary SF career in the making.