Beneath London, the tunnels are alive. Every day millions of people hear the warning: Mind the gap. But very few know what it truly means. Deep below the rushing trains and crowded platforms of London lies a hidden world -- a secret society of mysterious creatures known as Gaps , born from the sparks of the Underground and the ancient energy sleeping in the tunnels below. For generations the Gaps have lived quietly in the shadows, keeping the delicate balance between the human world above and the strange forces that stir beneath the city. But that balance is beginning to break. When a young Gap named Mind discovers that the ruthless King Rat is gathering power in the darkest tunnels, an adventure begins that will lead through forgotten stations, hidden chambers, and dangers no Gap has ever faced before. To protect his people, Mind must step forward as a leader -- even if it means risking everything.

Because if the tunnels fall into darkness, the world above may never be the same again. Next time you hear the warning. listen carefully. It might be meant for more than passengers.