ther
words, I am disposed to believe that he himself represents the most
recent outrage of what we will call 'The Scorpion.' Even at the time
that the body of the man found by the River Police had not been
identified, the presence upon his person of a fragment of gold
strongly resembling the tail of a scorpion prompted me to instruct
Inspector Dunbar to consult you. I had determined upon a certain
course. The identification of the dead man with Gaston Max merely
strengthens my determination and enhances the likelihood of my idea
being a sound one."

He flicked the ash from his cigarette and resumed:

"Without mentioning names, the experts consulted in the other cases
which--according to the late Gaston Max--were victims of 'The
Scorpion,' do not seem to have justified their titles. I am arranging
that you shall be present at the autopsy upon the body of Gaston Max.
And now, permit me to ask you a question: are you acquainted with any
poison which would produce the symptoms noted in the case of Sir Frank
Narcombe, for instance?"

Stuart shook his head slowly.

"All that I know of the case," he said, "is that he was taken suddenly
ill in the foyer of a West-End theatre, immediately removed to his
house in Half Moon Street, and died shortly afterward. Can you give me
copies of the specialists' reports and other particulars? I may then
be able to form an opinion."

"I will get them for you," replied the Commissioner, the exact nature
of whose theory was by no means evident to Stuart. He opened a drawer.
"I have here," he continued, "the piece of cardboard and the envelope
left with you by the missing cab-man. Do you think there is any
possibility of invisible writing?"

"None," said Stuart confidently. "I have tested in three or four
places as you will see by the spots, but my experiments will in no way
interfere with those which no doubt your own people will want to make.
I have also submitted both surfaces to a microscopic examination. I am
prepared to state definitely that there is no writing upon the
cardboard, and except for the number, 30, none upon the envelope."

"It is only reasonable to suppose," continued the Commissioner, "that
the telephone message which led Inspector Dunbar to leave your house
last night was originated by that unseen intelligence against which we
find ourselves pitted. In the first place, no one in London, myself
and, presumably, 'The Scorpion' excepted, knew at that time that M.
Gas