"I have always insisted, Smith," I cried, "that there was danger! What of poisoned darts? What of the damnable reptiles and insects which form part of the armoury of Fu-Manchu?" "Familiarity breeds contempt, I suppose," he replied. "But as it happened, none of those agents was employed. The very menace that I sought to avoid reached me somehow. It would almost seem that Dr. Fu-Manchu deliberately accepted the challenge of those screwed up windows! Hang it all, Petrie! one cannot sleep in a room hermetically sealed in weather like this! It's positively Burmese; and although I can stand tropical heat, curiously enough the heat of London gets me down almost immediately." "The humidity; that's easily understood. But you'll have to put up with it in the future. After nightfall our windows must be closed entirely, Smith." Nayland Smith knocked out his pipe upon the side of the fireplace. The bowl sizzled furiously, but without delay he stuffed broad-cut mixture into the hot pipe, dropping a liberal quantity upon the carpet during the process. He raised his eyes to me, and his face was very grim. "Petrie," he said, striking a match on the heel of his slipper, "the resources of Dr. Fu-Manchu are by no means exhausted. Before we quit this room it is up to us to come to a decision upon a certain point." He got his pipe well alight. "What kind of thing, what unnatural, distorted creature, laid hands upon my throat to-night? I owe my life, primarily, to you, old man, but secondarily, to the fact that I was awakened, just before the attack, by the creature's _coughing_--by its vile, high pitched _coughing_...." I glanced around at the books upon my shelves. Often enough, following some outrage by the brilliant, Chinese doctor whose genius was directed to the discovery of new and unique death agents, we had obtained a clue in those works of a scientific nature which bulk largely in the library of a medical man. There are creatures, there are drugs, which, ordinarily innocuous, may be so employed as to become inimical to human life; and in the distorting of nature, in the disturbing of balances and the diverting of beneficent forces into strange and dangerous channels, Dr. Fu-Manchu excelled. I had known him to enlarge, by artificial culture, a minute species of fungus so as to render it a powerful agent capable of attacking man; his knowledge of venomous insects has probably never been paralleled in the history of the world; whilst, in the sphere of pure toxicology, he had, and has, no rival: the Borgias were children by comparison. But, look where I would, think how I might, no adequate explanation of this latest outrage seemed possible along normal lines. "There's the clue," said Nayland Smith, pointing to a little ash-tray upon the table near by. "Follow it if you can." But I could not.