ug store on Sixth
Avenue. Duvall took a look at the apparently unconscious woman, then
spoke quickly to the chauffeur.

"Stay here until I return," he said. "Don't go away under any
circumstances. I shall be gone but a moment."

The man nodded.

"I'll stay, sir," he said. "Don't worry."

Duvall went quickly into the store. Going up to the soda counter, he
instructed the clerk to prepare him a dose of aromatic spirits of
ammonia as quickly as possible. While waiting for it, he watched the cab
through the store window.

The preparation of the dose required but a few moments. Then, explaining
matters to the clerk, Duvall took the glass in his hand and went back to
the cab. He smiled to himself at his anxiety, as he passed through the
door. The woman was far too ill, he reflected, to entertain any thoughts
of escape.

"Here," the detective said, opening the door of the cab. "Drink this."

There was no response. Duvall stuck his head into the vehicle with some
misgivings. Then he experienced a sudden and most mortifying shock.
There was no fainting woman huddled against the cushions in the far
corner. There was no woman at all. _The cab was empty!_

CHAPTER XI

Richard Duvall had had charge of many unusual and intricate cases, in
the past, and he prided himself upon the fact that he had handled them
with skill and discretion, and that the results which had followed had
been both quick and decisive. But in all his career he had not, so far
as he could remember, ever felt quite so chagrined, as he did when he
threw open the door of the cab and found that the woman he had left
there had disappeared.

The fault was his, he knew that well--entirely and unmistakably his.
This woman was evidently far more clever, more subtle than he had
imagined. He realized now that she had in all probability not taken the
drug he had given her in the dressing room of the theater, that she had
seen his effort to examine the contents of her handbag, that her
weakness, her call for a stimulant of some sort had been but clever
acting, and that she had purposely sent him into the drug store in order
that she might escape. He blamed himself, utterly and completely, for
his amazing stupidity in not realizing that the woman, instead of
ordering the cabman to drive away, had only to slip out through the door
on the opposite side of the vehicle, and vanish in the darkness.

And this she had quite evidently done. The door of the cab op