This summer everyone is at Piney Point, Grandmary's home in the mountains. Admiral Archibald Beemis has come all the way from England, as he does every summer. And Uncle Gard and Aunt Cornelia have brought the mischievous twins Agnes and Agatha with them. Samantha and the twins love to explore. One day they find an old sketchbook made long ago by Samantha's mother. It shows them something Samantha had forgotten - a waterfall she visited with her parents before they drowned in a boating accident. Using the sketchbook as their map, Samantha and the twins head off for Teardrop Island. When their secret exploration puts them in the middle of a dangerous storm, Samantha must save the day.