Sparrow is cold, hungry and alone, trudging through the grey streets of London. He spends his days looking hopefully for food and shelter, and his nights huddled miserably in dark alleys, shivering in the night air. He dreams of a better life, somewhere warm and dry, with lots of friends for company and plenty of food for all. His life changes when he meets Jimmy, who shows him a new life underground. A group of gifted children have created a society...