He regarded me steadily, without speaking. I saw that he realised my steadfastness of purpose, and that I meant to reveal the truth to all the world. "But," he cried at last, "you surely will not act as a fool, Holford! I told you on the night we first sat together of the great issues that depended upon your silence, and I repeat it now." "Why did you entice me into this complicated tangle of crime and mystery?" I demanded quickly. "Tell me that." "Because--well--" And he hesitated. "Because I--I was a fool--I admit it frankly. I ought never to have approached you. Three days later I regretted it deeply." "Regretted it because you found, to your surprise, that you had no fool to deal with!" I cried. "No; because I had made a mistake in another direction. But--but, hark?" I listened and heard a footstep outside on the stairs. "The Professor!" Kirk exclaimed. "He has returned. I'll introduce you." I rose from my chair, my teeth set together, my hand gripping the edge of the table. An instant later the door opened, and I stood boldly face to face with the impostor. Kirk, with that calm suavity of manner that so annoyed and irritated me, introduced us. But I bowed coldly to the well-dressed, elderly impostor, a man with keen, deep-set eyes, and a short, scrubby grey beard, asking of my companion: "Is this farce really necessary, Mr. Kirk, when I know the truth?" The new-comer looked askance at his accomplice, who gave him a quick, meaning look. "Ah! my dear Mr. Holford!" exclaimed the bogus Professor, "I've been most anxious to meet you for a considerable time. This is a great pleasure." "And one which I most heartily reciprocate," was my hard reply. "I've been endeavouring to find you for a long time. I followed you in Edinburgh, in Glasgow, and later on in Birmingham." "Then surely it is a rather happy circumstance that we have met to-day?" he said, rather fussily. "Happy for me, but perhaps unhappy for you!" I replied, with a dry laugh. "Why?" "Because I now intend to expose your very clever plot. The secret you have sold to Sir Mark Edwards does not belong to you at all, but to Professor Ernest Greer, the man who was killed in the room yonder--in his own laboratory!" His lips grew paler and set themselves hard. I saw in his dark eyes an expression of fear. He held me in terror--that was quite plain. "Holford, you are mistaken," declared Kirk. "In what way?" I demanded. "Professor Ernest Greer stands before you!" "No!" I cried. "This man is the impostor--the impostor who wrote to my wife, and enticed her from her home." "I wrote to Mrs. Holford, certainly," was the fellow's cool reply. "But without any evil intent; of that she will herself assure you." "Where is she?" "You will, no doubt, see her before very long, and she will explain the reason of her absence."