Ibbotson, master of the “poor orphan makes good” tale, offers another eminently satisfying example, this one wrapped in a valentine to Vienna, the author’s natal city. Raised by servants to be “a person who was interested in doing things, not having them,” 11-or-so-year-old foundling Annika sees a dream come true when lovely, regal Edeltraut von Tannenberg appears at the door one day, joyously announcing that she’s her real mother. Blinded by adoration, Annika barely notices how badly in need of repairs is her fortress-like new home, or how poorly she fits in with her spoiled and predatory new “family.” Readers will, though, as piece by piece, the author reveals an elaborate, clever fraud involving faked documents, smoothly plausible lies, and a hoard of supposedly imitation jewelry that Annika has inherited from an elderly neighbor. Creating suspense by letting readers into the scheme long before Annika and her friends, Ibbotson also paints a vivid picture of pre-WWI Vienna, from its delectable pastries to the famed show horses of the Spanish Riding School. Along with this beguiling atmosphere and expertly developed plot, readers will long remember the admirable Annika and cheer her eventual, well-deserved, triumph. Illustrations not seen. (Fiction. 10-13)