Julie Teller struggles with her emotions as her parents' impending divorce looms over her like a dark cloud. Having been sent to the seaside town of Bar Harbour, Maine to spend the summer with her grandparents, she feels abandoned, confused, and helpless. Though she contemplates what the future will hold for her, she doesn't anticipate what the summer will bring. Upon discovering a secluded cove, she finds a place of refuge where she can build sandcastles and be alone with her thoughts. When she sees signs of an intruder, however, she sets out with vigor to chase away the unwelcome visitor....