The Invisible Intruder Author:Carolyn Keene Old paperback. It was a beautiful day. Nancy & Ned had gone a quarter of a mile upstream, when Nancy exclaimed, "Ned! The self-paddling canoe is just ahead of us". They began to paddle at breakneck speed after it. This time, would they find the place where the mystery craft was hidden? Suddenly Nancy and Ned found it almost impossible to paddle... more ». It seemed as if some terrific pressure were pulling them backwards. The next moment, the canoe overturned, and the two plunged deep into the lake....« less