"Well, that Mabel one morning received a note delivered by express messenger, and I asked her whom it was from. She seemed unusually flurried, and told me that it was from Professor Greer." "But she never knew him!" I gasped. "What day was that?" "The day before you returned from Glasgow." "The same day on which she received that telegram from Italy purporting to be signed by me!" I exclaimed. "Why didn't you tell me this before, Gwen?" "Mabel's affairs have nothing to do with me. I am not interested in her correspondents, Harry," she replied. "Surely it is not my place to carry tales to you, is it?" "No; pardon me," I said, hastening to excuse myself, "but in this affair the truth must be told." "Then why haven't you told it to me?" asked the girl. "Why are you so carefully hiding other facts?" "Because they are of concern only to myself--a secret which is mine, and mine alone." "And it does not concern Mabel?" she demanded. "No," I replied hoarsely, "except that her acquaintance with the Professor has placed a new phase upon the mystery. Tell me all that happened concerning that note." "It came about eleven o'clock in the morning," she said. "I saw a telegraph-boy come up the steps, and believed he had a message from you. Annie took the note and brought it here into the dining-room, where Mabel signed for it. She read it through, and I saw that it caused her a great shock of surprise. Her hands were trembling. I inquired what was the matter, but she made some evasive reply. I demanded to know whom it was from, and she replied that her correspondent's name was Greer. `He ought never to have written to me,' she added. `Men are sometimes most injudicious.' Then she rose and placed the letter in the flames, watching it until it had been burned." "And is that all?" I demanded, astounded at the girl's story. "Yes, except that for some hours afterwards she seemed very upset. To me it appeared as though she had received word of some unusual occurrence. At noon she called a taxi by telephone, and went out. She did not return for luncheon, so I was alone. At three she came back, and I saw that she looked pale and distressed, while her eyes were red, as though she had been crying. But I attributed that to our ignorance of where you were. You know, Harry, how upset she is if when you are away you don't write or wire to her every day," added the girl. The story held me utterly speechless. That Mabel was acquainted in secret with the Professor astounded me. But it had been the false Professor who had written to her. Possibly the fellow was already in London while I was searching for him in Glasgow, and, if so, what was more probable than that she should have met him by appointment?