uld come into contact with one of the impregnated points."

"It was certainly a most fiendish plot!" I declared. "And I thank you,
Professor, for taking all this trouble with your analysis and so
establishing the truth. I will go to the police and inform them."

"Yes. I wish you to do that, for the fellow is undoubtedly in
possession of orosin, and intends to use it. Perhaps he has already
killed people by the same subtle and secret means."

"He must be arrested at all costs," I said. "Already the police all
over Spain are watching for him, and special surveillance is being
kept along all the railways and on the frontier."

"Any person with orosin in his possession should be detained and
examined," the Professor declared. "I wonder where he obtained it?"

"Who knows?" I exclaimed, but I was reflecting whether, after all, my
presence in Madrid was not known to De Gex. If so, was it possible
that he had hired the notorious Despujol to attack me in secret!

"Of course we know that there is a secret traffic in poisons.
Medico-legists, with the police, have established that fact over and
over again," said Professor Vega. "But the vendors are very difficult
to trace. One was found only six months ago--a doctor living in a
suburb of Copenhagen. But orosin is not known to a dozen people beyond
those who study toxicology. Hence this man Despujol must have been
supplied with it by someone who knew."

The suspicion had arisen in my mind that De Gex and his agent Suzor
knew that I was in Madrid for the purpose of watching them, and they
had resorted to a very clever and secret means of getting rid of me
once and for all. If the notorious criminal Despujol was in their pay
he would no doubt afterwards blackmail them, now that the desperate
plot had failed. Again, could it be possible that Moroni had had any
hand in supplying this most effective and dangerous of all secret
poisons to the Spanish malefactor who snapped his defiant fingers
under the very nose of the police?

As I sat in that quiet room of the Professor's, a room that smelt
strongly of chemicals, though it was filled mostly with books, I could
not refrain from shuddering when I reflected upon the narrow escape I
had had. Yet if De Gex resorted to such measures, he must certainly
hold me in great fear. Besides, if my life was threatened, so also was
that of my friend Harry Hambledon, who remained so vigilant in the
serene belief that his presence was undetected.