The shadow beast - Justin Richards

London, Today: Arthur Drake is beginning to understand how he is linked to the boy who wrote the Invisible Detective's casebook over eighty years ago. But there's no time to investigate further - a monster is loose in London, and Arthur must get help from the past...
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 - the ones who created him.

How can a daring bank robbery be linked to a missing cat? Why are the local rats overrunning houses and attacking people? Where will the trail of discarded bank notes lead? It seems that only the Invisible Detective can discover the answers as the kids hunt for the robbers - and track down a monster...