detectives.

It was not the duty of the latter, of course, to accompany or follow
anybody leaving the house unless they were called. Hence it was quite
possible for any of the guests to start out alone and make a trip to
any part of the city without the protection of a watchful guard. The
possibility that any of the guests might desire to take such a course
did not occur to Marion or any other member of the household. It was
presumed that everybody would gladly accept such protection on every
occasion when it seemed advisable.

As a matter of fact, however, the detectives had little to do on
Saturday and Sunday. Only three of the girls made shopping trips on
Saturday and all took an automobile ride Sunday afternoon. This was
the sum total of their activities away from the Stanlock home, with
the exception of one instance, of which there was no hint until late
in the afternoon.

About six o'clock Marion suddenly became mindful of the fact that she
had not seen Helen since their return from the automobile drive three
hours earlier, and she began a search for her. She first went upstairs
to her room to see if her friend were there. Probably she was tired
and had lain down to rest and fallen asleep. But an inspection of the
room failed to discover Helen.

Considerably puzzled, Marion now hunted up every other person in the
house and inquired for the missing girl. Not one of them remembered
seeing her since the return from the drive. The girl hostess was now
thoroughly alarmed and her fears were speedily communicated to the
others. Everybody joined in the search and every nook and corner
capable of concealing a human form was examined.

Helen Nash was not in the house and there seemed to be no reasonable
explanation of her disappearance.

* * * * *

CHAPTER XIII.

"FIND HER, OR I'LL FIND HER MYSELF."

Mr. Stanlock came home from a meeting of mining stockholders about the
time when consternation over the disappearance of Helen was at its
height. After the particulars of the affair, so far as they were
known, had been explained to him, he asked:

"Where are the detectives?"

The question fell with something of a shock on the ears of the
assembled searchers who had just completed a second fruitless hunt
through the house. Why had they not thought of the trio of "mystery
masters" before?

"We ought to have called them in at once," Mrs. Stanlock said. "I
suppose they've gon