"Poison and shock. The inhalation of certain poisons has a particularly deadly effect on people suffering from cardiac defection." "Could the poison have been self-inflicted? Are people suffering with such a disease prone to suicide?" "Only, as a rule, when the disease is in a very advanced state--you then get delirium, hallucinations, and morbid impulses." "And none of these symptoms were noticeable in the deceased?" "Not in a sufficiently marked degree to warrant the suggestion of suicide." "Have you no theory?" The doctor shook his head. "None whatever," he said; "and yet I'm sorry to say I can't help feeling there is something very sinister about it all--something that bodes ill for Sir Eldred." Much disappointed, I returned to the Caspar Beeches, and was making another inspection of the room in which one of the tragedies had occurred when, chancing to glance at the mirror over the mantelshelf, I caught the reflection of a pair of dark eyes fixed inquiringly at me. I looked round, and a figure passed along the passage. It was Mrs. Parry. She had evidently been peeping at me through the slightly open door, which I could have sworn I had closed. This made me careful. If I meant to unravel this mystery, I must on no account be seen doing anything that might arouse suspicion as to my real identity. Hence I determined to confine myself more to the study in future, and the rest of the morning I spent taking down in shorthand letters which Sir Eldred dictated. Walls have ears, and the sound of Sir Eldred dictating to me, I argued, might prove convincing. A week passed and I discovered nothing. There was nothing in the demeanour of any of the servants to give me the slightest reason for suspecting them; if any of them were "in the know" they kept their secret absolutely to themselves. At night, as soon as I deemed it safe, I slipped on a pair of rubber shoes and crept about the house and grounds, but with no result. On the morning of the eighth day I received two letters--one from Vane, who had taken furnished apartments next door to the house I had noted in the Holdenhurst Road, and the other from Craddock, the poison specialist. "I have at last found out something about those two people," Vane wrote. "They call themselves Effie and George Tyson. Tyson is an assumed name; the girl is the daughter of Parry, Sir Eldred's butler, and the man is Henry Mansfield, nephew of Sir Thomas." "Great heavens!" I could not help exclaiming. "This is news indeed. Sir Eldred assured me that he had no very near relatives." "Their bedroom is only separated from mine," the letter went on, "by a very thin wall, and when I had removed a brick I could catch every word they said. There's some mystery, and I'm going to try and solve it for you. Watch at the Beeches. I believe there is something extra in the wind. Effie has been there already this morning, and she and George are both going there again late this evening."