Sixteen-year-old Peggy has gone north to plant trees for the summer. On a visit to a petroglyph site, she is abruptly transported to Notherland, an imaginary world she created when she was seven. There, she learns that Mi, a spirit-child who lives in the northern lights, has gone in search of a mythical "shining world." Fearing for her safety, Peggy and her Notherland companions—Gavi the philosopher loon, Molly the pirate-doll, and a mysterious young man named Jackpine—set out in search of Mi.