That was four years ago, and from that day to this she has never seen or heard of them. She has travelled all over Europe and returned twice to America, has advertised in every possible way, and has employed the best detectives of both continents. Now she has come back for the third time, utterly broken in health and fortune. Their home in Philadelphia has become a boarding-house, and she has taken a room and will spend the rest of her life there, hoping that in that way, if they ever return, they may be able to reach her. Nearly all her money has gone in the search, and her mind is almost equally a wreck. She goes over to Philadelphia this afternoon, and I went in the morning to tell her good-by." Mary said--her lips were white--"But, good heavens, Emily! where could the girls have gone?" "That's the terrible part of it," Mrs. M---- answered. "One can't imagine. They were both so young. It was in a foreign country: they had no money. As far as the mother knew, neither had, nor could have had, any reason for going, nor anyone a reason for taking them. If one only had gone one might suspect a lover, or a sudden aberration of mind, but there were two; it was in broad daylight. Three minutes before they had been beside her. There was no struggle, no accident. No one could have silently carried off or made way with _two_ grown girls in Regent Street in midday. One minute they were there, laughing, happy, and commonplace, and the next minute they had vanished utterly and forever, without a word or a cry." "But why has one never heard of it?" I said. "Well, of course, the mother kept it out of the papers. For a long time she feared they might have been the victims of the sort of person who preys on young girls, and dreaded that there should be a scandal by which their lives should be ruined if they ever returned. To-day I think she would be glad to find them even in the lowest brothel, if she might only see them again." "Hadn't any of the police or detectives a theory?" "Oh, thousands at first, but they never bore any fruit. Consider all the circumstances. They were sensible, self-reliant American girls. By this time, if they were alive, they would have found some means of communicating with their mother. She has published guarded appeals, which they would understand, and always in the English language, in about every paper in this country and Europe." "But what do you think?" "What can one think? Can you conceive of any solution when you consider all the facts?" "Has the mother no theory?" "Well, she has, but then she is hardly sensible, you know, after the strain of such an experience. You've heard of the Fourth Dimension, haven't you? She says if that's not the explanation, she cannot imagine any other. She doesn't really believe it, I think, but she says if they did not stumble into it, where are they? And what answer can one give her?"