Twelve-year-old Marcie Horton isn't looking forward to spending a lonely and boring summer at her grandparents' lake cottage. Things take a turn for the eventful, however, when the woods near the cottage are threatened with development by the wealthy president of the university where Marcie's parents teach. Guided by the spirit of a Native American girl, Marcie must unlock the secrets of the past in her quest to save the centuries-old forest from destruction. Her efforts are complicated, though, by her growing friendship with the university president's popular daughter and the annual sailboat race, in which she finds herself competing on the team of the wealthy summer house owners against the local residents. Marcie's success hinges on whether she can decipher the cryptic messages she receives from the mysterious spirit of the Native American girl before the woods--and perhaps something much more important--are lost forever.