iece, and I could tell by the eagerness with which he peered
through it at the thumb-print that he was looking for something. A
moment later I felt sure that he had found that something which he had
sought, for, though he replaced the lens upon its nail with a quiet and
composed air and made no remark, there was a sparkle of the eye and a
scarcely perceptible flush of suppressed excitement and triumph which I
had begun to recognise beneath the impassive mask that he presented to
the world.

"I shall ask you to leave this little book with me, Mrs. Hornby," he
said, breaking in upon that lady's inconsequent babblings, "and, as I
may possibly put it in evidence, it would be a wise precaution for you
and Miss Gibson to sign your names--as small as possible--on the page
which bears Mr. Reuben's thumb-mark. That will anticipate any suggestion
that the book has been tampered with after leaving your hands."

"It would be a great impertinence for anyone to make any such
suggestion," Mrs. Hornby began; but on Thorndyke's placing his fountain
pen in her hand, she wrote her signature in the place indicated and
handed the pen to Miss Gibson, who signed underneath.

"And now," said Thorndyke, "we will take an enlarged photograph of this
page with the thumb-mark; not that it is necessary that it should be
done now, as you are leaving the book in my possession; but the
photograph will be wanted, and as my man is expecting us and has the
apparatus ready, we may as well despatch the business at once."

To this both the ladies readily agreed (being, in fact, devoured by
curiosity with regard to my colleague's premises), and we accordingly
proceeded to invade the set of rooms on the floor above, over which the
ingenious Polton was accustomed to reign in solitary grandeur.

It was my first visit to these mysterious regions, and I looked about me
with as much curiosity as did the two ladies. The first room that we
entered was apparently the workshop, for it contained a small
woodworker's bench, a lathe, a bench for metal work and a number of
mechanical appliances which I was not then able to examine; but I
noticed that the entire place presented to the eye a most unworkmanlike
neatness, a circumstance that did not escape Thorndyke's observation,
for his face relaxed into a grim smile as his eye travelled over the
bare benches and the clean-swept floor.

From this room we entered the laboratory, a large apartment, one side of
which was