The story begins with the disappearance of Benjamin in 2026 during his work on a project involving London's Post Office and an old underground railway. His sister Gabby and friends Peter and Freddie investigate, discovering an abandoned underground platform. Exposure to a mysterious gas transports them 230 years into the future, to 2256, where London is a silent, controlled city divided by social class and ruled by the Crown under President Hans Draggor. The city is patrolled by humanoid r...