On the Edge tells the story of Emerald Lake Visser, an unhappy fourteen-year-old who came to live on her aunt and uncle's farm when she was orphaned at age five. A misfit in her community and at school, her only real friend is an elderly woman, Jess, who teaches her to sail. Emma's a natural sailor, as if she's been on a sailboat her whole life. When Jess dies, it's revealed that she was Emma's grandmother. After receiving a letter that her mother may be living in the Bahamas, Emma runs away on her grandmother's boat, the Edge, to find her. Disguising herself as a boy, Emma sails the Edge through the Erie Canal, down the Hudson River, out onto the Atlantic Ocean and through the ICW to Miami, where she crosses the Gulf Stream to the Bahamas. Navigational mistakes, near misses with the coast guard, a robbery, and storms put Emma in danger time and again. To add to her stress, by the time she reaches New York City she suspects she's being followed. She notices small black pebbles appearing on her boat, along with dirty footprints in her cockpit. When a handwritten note is tucked into her porthole, she becomes very frightened. She has no passport and is underage. If she's caught, she'll be sent back to the farm. But Emma is determined to find her mother.