Lost within this unwelcoming place, Billy finds the companionship of two lonely children, Effie and Gus Mumford - one a science fair genius, the other a charming, silent bully. With a nearly forgotten bravery, Billy confronts the monotony of his job in telephone sales, the awkward beauty of a desperate pickpocket named Penny Maple, and the seemingly impossible solution to the mystery of his sister's death. Along the path laden with hidden clues and codes that dare to be deciphered, the boy detective may learn the greatest secret of all: the necessity of the unknown.