Invisible Detective

A daring bank robbery leads the Invisible Detective gang down into the sewers of London, where they discover a hideous beast whose master is the bank robber.

After finding a mysterious stone and an old casebook, fourteen-year-old Arthur finds himself remembering the 1936 adventures of a boy named Art who, under the identity of the Invisible Detective, works with three friends in London to solve the mystery of sinister puppets who are replacing real people.

While investigating a haunted house, the Cannoiers discover a group of scientists who are creating an army of indestructible mutant soldiers to fight the Germans in pre-World War II London.