“Well,” said Thorndyke; “what is it?”

“Aconite,” I replied without hesitation.

“Yes,” he agreed; “aconite it is, or more probably aconitine.  And that, I think, gives us all the information we want.  We need not trouble now to make a complete analysis, though I shall have a quantitative examination made later.  You note the intensity of the taste and you see what the strength of the solution is.  Evidently that lump of sugar contained a very large dose of the poison.  If the sugar had been dissolved in your tea, the quantity that you drank would have contained enough aconitine to lay you out within a few minutes; which would account for Mrs. Schallibaum’s anxiety to get clear of the premises.  She saw you drink from the cup, but I imagine she had not seen you turn the sugar out.”

“No, I should say not, to judge by her expression.  She looked terrified.  She is not as hardened as her rascally companion.”

“Which is fortunate for you, Jervis.  If she had not been in such a fluster, she would have waited until you had poured out your tea, which was what she probably meant to do, or have dropped the sugar into the milk-jug.  In either case you would have got a poisonous dose before you noticed anything amiss.”

“They are a pretty pair, Thorndyke,” I exclaimed.  “A human life seems to be no more to them than the life of a fly or a beetle.”

“No; that is so.  They are typical poisoners of the worst kind; of the intelligent, cautious, resourceful kind.  They are a standing menace to society.  As long as they are at large, human lives are in danger, and it is our business to see that they do not remain at large a moment longer than is unavoidable.  And that brings us to another point.  You had better keep indoors for the next few days.”

“Oh, nonsense,” I protested.  “I can take care of myself.”

“I won’t dispute that,” said Thorndyke, “although I might.  But the matter is of vital importance and we can’t be too careful.  Yours is the only evidence that could convict these people.  They know that and will stick at nothing to get rid of you—­for by this time they will almost certainly have ascertained that the tea-shop plan has failed.  Now your life is of some value to you and to another person whom I could mention; but apart from that, you are the indispensable instrument for ridding society of these dangerous vermin.  Moreover, if you were seen abroad and connected with these chambers, they would get the information that their case was really being investigated in a businesslike manner.  If Weiss has not already left the country he would do so immediately, and if he has, Mrs. Schallibaum would join him at once, and we might never be able to lay hands on them.  You must stay indoors, out of sight, and you had better write to Miss Gibson and ask her to warn the servants to give no information about you to anyone.”

“And how long,” I asked, “am I to be held on parole?”