"The young ladies spent the morning at a fashionable dressmaker's on Madison Avenue. I have picked up an acquaintance with a servant girl who lives in one of the flats in Thirtieth Street house, and from her I learn that Miss Remsen's new maid tells her that the affair at the Van Rawlston house will be a costume masquerade, all parties assuming characters from the Arabian Nights. Miss Emily Remsen will appear as Scheherezade. W----." Mr. Barnes turned two pages at this point, evidently considering that nothing of special moment was contained in the reports covering the next few days. He began again. "Dec. 30. Mr. Mitchel came out of his hotel at ten o'clock, and crossed over to Jersey City, taking an express for Philadelphia. I of course took same train. S----. "The Miss Remsens were at home all day. They are busy on their costumes for the coming entertainment. W----. "Dec. 31. Telegram from Philadelphia. 'Mitchel at Lafayette Hotel. Is sick in bed. Doctor in attendance. Sent a telegram to Miss Remsen telling her that he cannot be on hand to-morrow night.' S----. "Thauret went to Union Square costumer yesterday and obtained the Ali Baba costume ordered for Mitchel. He gave the costumer a letter which he had received from Mitchel, dated at Philadelphia yesterday. It reads: 'Friend Thauret, I am suddenly taken ill. Don't let the Remsens know that it is anything serious. Oblige me, if possible, by attending the Arabian Night festival. I enclose my invitation and a note to Mr. Van Rawlston, which will introduce you. You may wear my costume, and the costumer will give it to you if you present this. You were to have gone out of town I know, but if you wish to do me a favor I hope you will change your plans and take my place. I do not wish Miss Remsen to be entirely unattended. Therefore be with her as much as you can. She will be dressed as Scheherezade. '(Signed) Mitchel.' "I obtained this from the costumer by saying I am a detective shadowing a criminal. Q----." CHAPTER X. ALI BABA AND THE FORTY THIEVES. After reading the foregoing, Mr. Barnes carefully locked his diary in his cabinet, and immediately after left the house on his way to New York. Reaching there he proceeded up-town, finally ringing the door-bell of the Van Rawlston mansion. He requested to see the master of the house upon urgent business, and that gentleman soon presented himself. "Mr. Van Rawlston," said Mr. Barnes, "I am a detective. May I have a few moments of strictly private conversation with you?" "Certainly," was the reply. "Step into my study. We will be entirely safe from prying ears there." A moment later the two men were seated in comfortable leather chairs facing each other.