London, today: When fourteen-year-old Arthur Drake shelters from the rain in a dusty shop, the last thing he expects to find is the antique casebook of The Invisible Detective. It may have been written in the 1930s, but it's in his handwriting...London, 1936: Whatever your problem, the Invisible Detective can find the answer. He is a mystery, an enigma. In fact, the truth about the Invisible Detective is known by only four children with their own special talents. Together the children use their special skills to solve crimes and mysteries. But who'd listen to a bunch of kids? Now the gang is about to take on their most sinister case so far. When an incredible touring exhibition takes over their den, the Invisible Detective must deal with disappearing people, faceless bodies, and some deadly puppets...