"Mr. Van Rawlston," began the detective, "to explain my purpose at once, I have only to say that I desire your permission to attend the masquerade which will be held here to-night. I am aware that this must seem an odd request, but I make it entirely in your own interests." "If you will explain more fully, sir, I may be quite willing to grant your request," said the other. "You should know that a masquerade is a dangerous kind of entertainment. At such affairs large robberies have often been committed--the thieves operating boldly, and escaping through the aid of their disguises. I have good reason for believing that such a crime is contemplated to-night." "My dear sir, impossible! Why, no one will be admitted save those with whom we are well acquainted. Tickets have been issued by the society which gives the festival, and every one must unmask before being allowed to enter. Therefore, whilst I am grateful to you for your warning, I hardly think that I need your services." "Mr. Van Rawlston, I regret to say that you are mistaken. In the first place, your close scrutiny of all who enter will probably be relaxed as the night wears on. Again, there are ways of getting in unperceived, and once within, the thief would be unsuspected. But this is no guesswork on my part. I do not think, I know, that, unless I am here to prevent it, a robbery will be committed. Indeed, I may even fail to prevent it." "Why, sir, you speak as though you know the person who is to play the criminal." "I do. For several weeks my men have been watching certain suspicious parties. From data furnished by my spies, I am sure that plans have been perfected by which one or more of your guests will be robbed during the progress of the entertainment." "Still it seems incredible. As I have said, no one will be able to enter without our knowledge." "Of course, I cannot intrude upon you, Mr. Van Rawlston. But if you are obliged to appeal to the police to-morrow for the recovery of stolen property, you alone will be to blame if the thief shall have had several hours the start of us. I have warned you. That is the best I can do. I wish you good-morning." Mr. Barnes rose to go, but Mr. Van Rawlston stopped him. "One moment," said he. "If you are so sure that there is a scheme of robbery afoot, of course I must not be so rash as to refuse your aid. What do you advise? We could postpone the festival." "By no means. The course to pursue is to keep what I have told you strictly secret. In fact, if possible, dismiss it entirely from your mind, so that by your behavior the thief may not know that suspicions have been aroused. Do as I requested at first, and as I know my man I will be able to keep an eye upon him should he be present." "I suppose it must be as you say. But you must be in costume. I have it! The committee have ordered some costumes which they will give to those who come unprovided. You may have one of those." "What costume shall I ask for?"