ients, whose interests would suffer by
your death--to have this fellow laid by the heels before he does any
mischief."

"Yes; I shall have to interfere if he becomes really troublesome, but I
have reasons for wishing to leave him alone at present."

"You do really know who he is, then?"

"Well, I think I can solve the equation that I have just offered to you
for solution. You see, I have certain data, as you suggest, which you do
not possess. There is, for instance, a certain ingenious gentleman
concerning whom I hold what I believe to be exclusive information, and
my knowledge of him does not make it appear unlikely that he might be
the author of these neat little plans."

"I am much impressed," I said, as I put away my notebook, after having
jotted down the points that Thorndyke had advised me to consider--"I am
much impressed by your powers of observation and your capacity for
reasoning from apparently trivial data; but I do not see, even now, why
you viewed that cigar with such immediate and decided suspicion. There
was nothing actually to suggest the existence of poison in it, and yet
you seemed to form the suspicion at once and to search for it as though
you expected to find it."

"Yes," replied Thorndyke; "to a certain extent you are right. The idea
of a poisoned cigar was not new to me--and thereby hangs a tale."

He laughed softly and gazed into the fire with eyes that twinkled with
quiet amusement. "You have heard me say," he resumed, after a short
pause, "that when I first took these chambers I had practically nothing
to do. I had invented a new variety of medico-legal practice and had to
build it up by slow degrees, and the natural consequence was that, for a
long time, it yielded nothing but almost unlimited leisure. Now, that
leisure was by no means wasted, for I employed it in considering the
class of cases in which I was likely to be employed, and in working out
theoretical examples; and seeing that crimes against the person have
nearly always a strong medical interest, I gave them special attention.
For instance, I planned a series of murders, selecting royal personages
and great ministers as the victims, and on each murder I brought to bear
all the special knowledge, skill and ingenuity at my command. I inquired
minutely into the habits of my hypothetical victims; ascertained who
were their associates, friends, enemies and servants; considered their
diet, their residences, their modes of conveyan