. . . or was she? Just when friendless foster child Anna has decided that the girl in Marsh House was a mirage, the lively and gregarious Lindsays move in, and Scilla, who's also a dreamer, finds a diary, Marnie's diary, that corroborates the elusive encounters Anna had with her. But it all happened fifty years before. . . . Up to this point a plausible puzzle; thereafter a strangling denouement: elderly visiting artist Gillie knew Marnie as a child, provides clues that convince Mrs. Lindsay that Marnie was Anna's grandmother. No wonder Marsh House seemed familiar. . . . Defensive Anna thawing toward well-meaning foster mother Mrs. Preston and summer substitute Mrs. Pegg is easier to believe; Marnie's misery and the Lindsays' happiness, once understood, have changed her. A bubble but not entirely a bust.