Station Zero — Philip Reeve

What happens after the adventure of a lifetime? For Zen, it's a safe, comfortable life of luxury. But it's not what Zen wants. He misses the thrill of riding the rails, of dodging danger, and of breathing the air of different planets. Most of all of course he misses Nova ― lost to him forever in a distant world. But then one day a mysterious message arrives, and that's all Zen needs to head right off, ready for anything. Except that no one could be ready for what he finds... Thrilling, thought-provoking, and breathtaking, this finale to the Railhead trilogy weaves a web of wonder, full of characters and events you will never forget.