Everything is implausible about this except protagonist Monica's moment of self-reproach. We're asked to believe that 30 girls, age six to twelve, are spending their summer days in a select private school (for purposes unspecified); that, in this tiny resort community, another girl appears as soon as one departs; and, in a pile-up of juvenile-fiction staples, that overbearing, unappealing newcomer Rhoda is the daughter of an up-and-coming actress, the granddaughter of the resident witchy old woman, and the nearest neighbor of the local ""haunted house."" On the could-be side, popular Monica and her two good pals tolerate Rhoda without really taking her in--winning praise from schoolmistress Madame de Vere that they don't really merit. Then, more melodrama: Rhoda pretends to disappear in order to lure Monica to the environs of the haunted house and--""If you only knew how much I hated you. . . . The very first day you shut the door in my face""--proceeds to push her into the well. In the denouement, with unhappy Rhoda gone (presumably unaltered) and another girl in her place, Monica resolves that, ""whatever she is,"" ""I won't close the door."" The amount of fabrication is disproportionate to--and inconsistent with--that true-to-life tremor of remorse.