The other letter, from Craddock, was as follows: "There's only one gas that produces all the effects you describe," he said, "and that has certainly been hitherto unknown in England; indeed, the knowledge of it has been strictly confined to one region--a district in the south-east of Borneo. The natives there worship a great spirit, which they name the Arlakoo or Hell-faced one, and they never invoke it save when they desire the death of a criminal, or some very aged, useless member of the tribe. They then prepare a mixture of herbs and berries, which they first of all dry, and, at the psychical hour of two in the morning, put in an iron pot and take into the presence of their intended victim. Then, having set fire to the preparation, which, though rather difficult to ignite, burns slowly and surely when once aflame, they close all the openings of the hut or room and beat a precipitate retreat. A few minutes later the spirit they have invoked appears, and, simultaneous with its materialisation, the mixture burns a bright green and emits a peculiarly offensive gas. The result is invariably death: the shock produced by the harrowing appearance of the apparition, coupled with the poisonous nature of the fumes, is more than the human mechanism can stand. Of course all this would be mere moonshine to anyone who is uninitiated in Eastern ways and doesn't believe in ghosts. The Bournemouth doctors would pooh-pooh it altogether. There is no other gas that I know of that produces the effects you have described. If there is another case, let me know, as I should much like to see the victim." A ghost! A ghost employed for the purpose of murdering someone! Even to me, confirmed believer in the Unknown as I am, the idea seemed wildly improbable and fantastic. And yet, what else could have produced that look of horror in the faces? What else could have killed them? That evening, Sir Eldred and I sat in the smoke-room after dinner and chatted away as usual. We had our coffee brought to us at nine o'clock, and at ten-thirty we retired to bed. Sir Eldred had appeared fidgety and nervous all the evening, and, as we were ascending the stairs, he asked me if I would mind sitting up with him. "I feel I shan't sleep to-night," he said, "as I've got one of my restless moods on. If it won't be tiring you too much, will you come and sit with me?" I said I would with pleasure, but I did not join him at once, as I wanted the servants to think we had gone to our respective rooms and to bed as usual. I also wanted whatever there might be in the wind to mature. On entering my room, I opened the window with as little noise as possible, and was on the verge of lowering myself into the garden when I espied someone among the trees. I was going to draw back, when the figure signalled, and I at once knew it was Vane.