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?"

"Oh, they are all alike. They are the Forty Thieves."

"The Forty Thieves?" Mr. Barnes was surprised. "Is not that an odd
costume?"

"Oh, no! It was Mr. Mitchel's idea. He is the chairman of the committee.
He argued that rather than provide a lot of meaningless dominos, the
stragglers, who will be chiefly invited guests who are not members of
the society, may be thus garbed, and still fall into the scheme of the
evening, which is that every one shall play the part of some character
of the Arabian Nights."

"Very well, Mr. Rawlston, for once the detective will don the garb of a
thief. After all, you know the adage, 'it takes a thief to catch a
thief.'"

"Very good, Mr. Barnes--I believe that is the name on your card?
Yes--Well, come to-night early and you shall be fitted out. Later, if
you should wish to speak to me, I shall be dressed as the Sultan, a
character about as foreign to my true self as yours will be to you."

Mr. Barnes left the house thoroughly satisfied with the result of his
visit. In the first place he had learned something. Mr. Mitche