twenty years among the good people

Well, on second thought Doyle surely refers to a folktale, though I haven't found it. One folk tale that is almost exactly like cabin on the coast is "twenty years with the good people" in a folk tale collection by d. Knox. It too Involves father and son similarities but this time the father is the one taken for twenty years, and he won't talk about it when he comes back to his wife's house.