London, 1937: The Invisible Detective can solve any mystery, great or small - but no one's ever seen his face. Truth is, the detective is the creation of four extraordinary kids who combat crime in his name... Who is the misshapen figure stalking the streets after dark? When people start to die, the Invisible Detective is called in. But can Art and his friends find the inhuman killer before the killer finds them? The past is far from dead, as Arthur finds out when he wins the chance to spend a weekend at a country house. He may have won a competition, but he is in danger of losing everything - including his own life...