Pontifex Son and Thorndyke

This puzzling plot is related by two different characters: messenger boy Jasper Gray, who experiences several strange adventures, and Dr. Jervis, friend of Dr. Thorndyke. Dr. Thorndyke is investigating a terrible crime, the solving of which remains elusive because of key facts that remain unknown. He needs the facts to confirm his case: Jasper could complete the blank spaces if only Thorndyke were aware of his existence.