The empty yellow house on Grandpa Alden's island was shrouded in mystery for over forty years. When Grandpa tells Henry, Jessie, Violet, and Benny Alden of the curious circumstances in which the house became vacant, the children are not satisfied to leave the story unfinished. Determined to solve the mystery, the children uncover a trail of clues that lead them all the way to the woods of Maine. With Joe and his new wife, Alice, as guides, the children learn the ways of the wild--cooking on an open fire, catching fish for dinner, and making beds with evergreen boughs and blankets. More than once, the children are reminded of their boxcar days while piecing together the puzzle of the yellow house, until they reach the heartwarming conclusion.