The Traitor's Gate, by Avi, 2007

John Huffam's life as the son of a profligate London gentleman dissolves the day his family's belongings are seized and they're hauled to a "sponging house," their last stop on the way to debtor's prison. Strange people approach John's father, and still stranger ones follow John, for reasons that must go beyond mere gambling debts. This mystery, tour through Dickensian London, and love letter to Dickens introduces the memorable characters of Sary the Sneak and Mr. Snugsbe, great of coat and cauliflowered of hair. Recommended.