'(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.

"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