The author of the grand neo-Victorian trilogy begun with The Ruby in the Smoke (1987) creates a unique format for a thriller for younger children, also set in 19th-century London. Combining dialogue set in cartoon sequences with a substantial, action- packed text that manages to be easily accessible while parodying the likes of Dickens and throwing in some fat, euphonious vocabulary (``defenestrated''), he tells an entertaining story of three young siblings escaping from Mr. Killjoy and Miss Gasket at the Alderman Cawn-Plaster Memorial Orphanage. Other delightful villains include a violin-playing Mack the Knife; on the other side, the superhero of the title is ably assisted by the three kids, a nice young couple, and the persistent conscience of a gangster named Filthy. Mostyn's drawings, on virtually every page, have an energy and humor that rival David Small's best work. Hilarious, neatly plotted, and thoroughly appealing. (Fiction. 8-12)