"He learned mine easily enough, and would have learned yours. You seem to forget, Mr. Inspector, that we are dealing with a genius in the way of criminality. The Spider, whomsoever he may be, seems to know everything. I believe that he is the head of a gang and has his spies all over London. No one person could be so well posted up in secret arrangements otherwise." "How did he come to know of the secret arrangement between yourself and Mr. Dimsdale?" asked Drench abruptly. "I can't say, unless Mr. Dimsdale, who had rather a loose tongue, revealed his plan of the trap to someone else. I said nothing." "Mr. Dimsdale gave no information to anyone in this house," said Frances decisively; "if he had, either I or Ida would have known. As it is, he apparently met this dreadful person in the library at the agreed time. And, now that I think of it," she mused, "I wonder that I did not suspect something of the sort. Mr. Dimsdale told Ida and myself that we could have all the rooms for the ball save the library, as he wished that to himself." "There's nothing unusual in such a wish," remarked Drench easily. "When a house is upset by a party a man naturally wishes one of his rooms left undisturbed so that he can have peace." "What happened exactly?" asked Vernon with an air of fatigue. Inspector Drench signed that Miss Hest should explain, and glanced at his notes as she spoke, to be certain that she was repeating what she had already told him prior to Vernon's entrance. "It is hard to tell what took place to a minute," protested the lady. "Our guests arrived just before ten o'clock, and everything was going splendidly." "Everyone was masked, I suppose," said Vernon quietly. "Oh, yes. But Mr. Dimsdale stood in the Hall until nearly eleven, receiving our guests, and made everyone unmask before they entered the ballroom." "Why did he do that?" asked Drench suddenly. "Can't you guess?" put in Vernon impatiently. "Mr. Dimsdale expected The Spider, and wished to see if he would come." "But he didn't know what The Spider was like. No one knows." "I daresay. But Mr. Dimsdale knew those whom his daughter had invited to the ball. If an unknown person had unmasked he would have jumped to the conclusion, and perhaps truly, that he was The Spider. Well, Miss Hest?" "Everyone who unmasked were people we knew," she continued, "for I stood with Ida near Mr. Dimsdale, receiving the guests. At a quarter to eleven Mr. Dimsdale went to the library." "Alone?" "Certainly. No one, to my knowledge, entered the library during the whole of that evening until Ida, in search of her father, insisted upon going in, notwithstanding the prohibition, at a quarter to twelve. Then she found Mr. Dimsdale seated in his chair, quite dead." "Were the windows open?"