"I am showing you how I picked my own theory to pieces," he answered. "I next considered the visitors. I assumed they were there for an unlawful purpose--your facts go to show that my assumption was right--and I asked myself why and how they had murdered Bridwell. If he were a schemer with them, there would be no need to murder him, no need to silence him; were he to talk afterwards he would only injure himself, not them. If they were there to force papers from their host, it seems unlikely that he would be so unsuspicious of them that he would have asked them to dinner, and, even if he were, a moment must have come during, or after dinner, when they must have shown their hand. A man who deals in this kind of commerce does not easily trust people. Bridwell's suspicions would certainly have been aroused; he would in some measure, at any rate, have been prepared, and we should have found some signs of a struggle." "I admit the soundness of the argument," I answered. "For my part I incline to Reynolds' opinion that it was suicide after all." "Oh, no; it was murder," said Quarles. "A tablet--" I began. "I know it was murder," returned the professor sharply, "and the manner of it has presented the chief difficulty I have found in demolishing my theory altogether. Bridwell was poisoned by an injection. The hypodermic needle was inserted under the hair at the back of the head, here in the soft part of the base of the skull, the hair concealing the small mark it made. I believe the secret of the poison used is forgotten, but you may read of it in books relating to the Vatican of old days and concerning the old families of Italy. I might mention the Borgias particularly. So you see my difficulty, Wigan. The crime literally reeked of Italy, and we had two Italians amongst our dramatis personae." "A significant fact," I said. "Of course I am letting the doctor know of my discovery; that is the good turn I shall do him. He will be considered quite smart over this affair. Now consider this point. It would surely have been very difficult, once the host's suspicions had been aroused, to make the injection without a struggle on the victim's part." "No suspicion may have been aroused," I said. "Masini has told us of a map. The murderer might have been leaning over his victim examining it." "That is true. You pick out the weak point," said Quarles. "Even then there would have been some sort of struggle, surely," said Zena. "The poison can hardly act instantaneously."