"But he came with a visiting-card," I said. "He went to the firm of engineers who are making certain alterations in my monoplane, and demanded of the foreman the right to examine what was in progress. He told them at Willesden that he was an official of your Department, sent by you, with authority from myself." "Well, Mr Munro," replied the professor, in that quiet, matter-of-fact way of his, "this is the first I've ever heard of any Mr Hale. He certainly has never been sent by us. In fact I was entirely unaware, until this moment, that you had any experiments in progress." "Really, professor, I'm awfully sorry to trouble you," I said. "But I'm only trying to do my little bit--my very small bit--in the war. Thank you for telling me this. One never knows when one meets enemies. The Germans are so clever, so practical, and so subtle." "They are," he answered. "Be wary, my dear Munro. If you are carrying out experiments upon any extensive scale you may be quite certain that somebody in enemy pay is watching. I have long seen it--long before the outbreak of war." Here again we had come up against the dead wall of fact. "Then you think that the stranger was an enemy spy?" I asked. "Well, in face of the facts, and of what I myself know, I'm perfectly certain of it," the professor said. "I have no knowledge whatever of any person called Harold Hale. He evidently went out to Willesden to try and obtain certain knowledge, yet, by the sturdy attitude of the foreman whom you mention, he was defeated. Truly the wily and dastardly plots of our dear-brother-Germans--as they were called by some irresponsible Englishmen those hot August days of the declaration of war--have been amazing. It seems to me, Munro," added the voice over the wire, "that if you are wary and watchful you may discover something that may be of unusual interest to the Intelligence Department." Then in my ear there was a loud buzz, followed by a sharp click, and all became silent. CHAPTER SIXTEEN. AT HOLLY FARM. Those constant proofs of the enemy's eager inquisitiveness were, I here freely admit, very disconcerting. We seemed surrounded by spies. A dastardly attempt had been made to kill me, while some evil--what, I knew not--had happened to my well-beloved. It often struck me as most peculiar why she should preserve that strict secrecy regarding her whereabouts through those weeks when she had been missing. Her terror of the mysterious woman whom she so constantly described as possessing the eyes of a leopard, together with the unbalanced condition of her brain, were, in themselves, solid proof that she had passed through some horrifying and terrible experience. Besides, had she not admitted that she had existed in what she herself had termed "a living tomb?"