. He worked with closed windows in the hottest weather. There
is no other door, for the study occupies the end of a narrow wing, so
that no one could possibly have gained access to it, whilst I was in
the library, unseen by me. Had someone concealed himself in the study
earlier in the evening--and I am convinced that it offers no
hiding-place--he could only have come out again by passing through
here."

Nayland Smith tugged at the lobe of his left ear, as was his habit when
meditating.

"You had been at work here in this way for some time?"

"Yes. Sir Crichton was preparing an important book."

"Had anything unusual occurred prior to this evening?"

"Yes," said Mr. Burboyne, with evident perplexity; "though I attached
no importance to it at the time. Three nights ago Sir Crichton came
out to me, and appeared very nervous; but at times his nerves--you
know? Well, on this occasion he asked me to search the study. He had
an idea that something was concealed there."

"Some THING or someone?"

"'Something' was the word he used. I searched, but fruitlessly, and he
seemed quite satisfied, and returned to his work."

"Thank you, Mr. Burboyne. My friend and I would like a few minutes'
private investigation in the study."

CHAPTER II

SIR CRICHTON DAVEY'S study was a small one, and a glance sufficed to
show that, as the secretary had said, it offered no hiding-place. It
was heavily carpeted, and over-full of Burmese and Chinese ornaments
and curios, and upon the mantelpiece stood several framed photographs
which showed this to be the sanctum of a wealthy bachelor who was no
misogynist. A map of the Indian Empire occupied the larger part of one
wall. The grate was empty, for the weather was extremely warm, and a
green-shaded lamp on the littered writing-table afforded the only
light. The air was stale, for both windows were closed and fastened.

Smith immediately pounced upon a large, square envelope that lay beside
the blotting-pad. Sir Crichton had not even troubled to open it, but my
friend did so. It contained a blank sheet of paper!

"Smell!" he directed, handing the letter to me. I raised it to my
nostrils. It was scented with some pungent perfume.

"What is it?" I asked.

"It is a rather rare essential oil," was the reply, "which I have met
with before, though never in Europe. I begin to understand, Petrie."

He tilted the lamp-shade and made a close examination of the scraps of
pap