Perhaps the research material that has been most helpful to me during the writing of “The Boy Sherlock Holmes” series has not been a book but a map. Edward Stanford’s Library Map of London and Its Suburbs, 1862, a virtual aerial photograph of the great city in a time before such things existed, has been my constant companion and invaluable ally. This novel, like the others, finds Sherlock scurrying about London, and my map has always kept him in the right place, even situated him under real trees in their correct locations. Leslie S. Klinger’s The New Annotated Sherlock Holmes, in three volumes has also been irreplaceable, helping me to see clearly into Sir Arthur Conan Doyle’s creation and his stories, to add depth to my understanding of the time period in which my tales are set. Charles Dickens appears several times in this series, perhaps most prominently in this book. Observing brilliant British actor Simon Callow’s recreation of him on the stage and screen helped me to accurately recreate him here, as did Peter Ackroyd’s masterful biography, Dickens. At Tundra Books, I continue to be indebted to the brilliant editorial work of Kathryn Cole, an untiring colleague during every Boy Sherlock installment so far, and hopefully for the next and last, as well. Pamela Osti, Sylvia Chan, Jennifer Lum, and Derek Mah all remain big parts of The Boy Sherlock team. And on the home front, I’d like to thank the kids in the house and the other grown-up, Sophie, who listen to every word of each manuscript and let me know when it is fit to go out into the world.