"But that experiment I have just witnessed? Has it no connexion with the mystery?" "Yes, some slight connexion. It was, however, a failure," he grunted, still speaking with his strong accent. "You experienced the same sensation there to-day, I hear?" I said. "H'm, yes; but not so strong." "And the same injection cured you?" "Of course. That, however, tells us nothing. We cannot yet ascertain how it is caused." "Or find out who was that unknown woman in black," I added. "If we could discover her we might obtain the key to the situation," he responded. "I have been invited by her ladyship to visit them in Wiltshire," I said suddenly, as I lit a cigarette, "and I have accepted. Have I done right, do you think?" "You would have done far better to stay here in London," grunted the old man. "If we mean to get at the bottom of this mystery we must work together." "How?" "In this affair, my dear Colkirk," he exclaimed, with a sudden burst of confidence, "there is much more than of what we are aware. There is some motive in getting rid of Miss Wynd secretly and surely. I feel certain that she knows who her mysterious visitor was, but dare not tell us." "I am going down to Atworth," I said. "Perhaps I shall discover something." "Perhaps?" he sniffed dubiously. "But, depend upon it, the key to this problem lies in London. You haven't yet told me who this Miss Wynd is." "A lady who, her father being dead, went to live with Sir Henry Pierrepoint-Lane and his wife." "Ach! then she has no home? I thought not." "Why? What made you think that?" "I fancied so," he said, continuing to puff at his great pipe. "I fancied, too, that she had a lover--a young lover--who is a lieutenant in a cavalry regiment." "How did you know?" "Merely from my own observations. It was all plain last night." "How?" But he grinned at me through his great ugly spectacles without replying. I knew that he was a marvellously acute observer. "And your opinion of her ladyship?" I inquired, much interested. "She, like her charming cousin, is concealing the truth," he answered frankly. "Neither are to be trusted." "Not Beryl--I mean Miss Wynd?" "No; for she knows who her visitor was, and will not tell us." Then he paused. In that moment I made a sudden resolve; I asked him whether he had read in the newspapers the account of the Whitton tragedy. "I read every word of it," he responded--"a most interesting affair. I was not well at the time, otherwise I dare say I might have gone down there." "Yes," I said, "from our point of view it is intensely interesting, the more so because of one fact, namely, that her ladyship was among the visitors when the Colonel was so mysteriously assassinated." "At Whitton!" he exclaimed, bending forward. "Was she at Whitton?" "Yes," I answered. "And her cousin, Miss Wynd?"