“You do not believe it?  I tell you it is so.  The girl herself as good as acknowledged it to me.”

I spoke slowly and distinctly.  “Dr. Sebastian,” I said, confronting him, “let us be quite clear with one another.  I have found you out.  I know how you tried to poison that lady.  To poison her with bacilli which I detected.  I cannot trust your word; I cannot trust your inferences.  Either she is not Yorke-Bannerman’s daughter at all, or else . . .  Yorke-Bannerman was not a murderer. . . .”  I watched his face closely.  Conviction leaped upon me.  “And someone else was,” I went on.  “I might put a name to him.”

With a stern white face, he rose and opened the door.  He pointed to it slowly.  “This hospital is not big enough for you and me abreast,” he said, with cold politeness.  “One or other of us must go.  Which, I leave to your good sense to determine.”

Even at that moment of detection and disgrace, in one man’s eyes, at least, Sebastian retained his full measure of dignity.

CHAPTER VI

THE EPISODE OF THE LETTER WITH THE BASINGSTOKE POSTMARK

I have a vast respect for my grandfather.  He was a man of forethought.  He left me a modest little income of seven hundred a-year, well invested.  Now, seven hundred a-year is not exactly wealth; but it is an unobtrusive competence; it permits a bachelor to move about the world and choose at will his own profession. I chose medicine; but I was not wholly dependent upon it.  So I honoured my grandfather’s wise disposition of his worldly goods; though, oddly enough, my cousin Tom (to whom he left his watch and five hundred pounds) speaks most disrespectfully of his character and intellect.

Thanks to my grandfather’s silken-sailed barque, therefore, when I found myself practically dismissed from Nathaniel’s I was not thrown on my beam-ends, as most young men in my position would have been; I had time and opportunity for the favourite pastime of looking about me.  Of course, had I chosen, I might have fought the case to the bitter end against Sebastian; he could not dismiss me—­ that lay with the committee.  But I hardly cared to fight.  In the first place, though I had found him out as a man, I still respected him as a great teacher; and in the second place (which is always more important), I wanted to find and follow Hilda.

To be sure, Hilda, in that enigmatic letter of hers, had implored me not to seek her out; but I think you will admit there is one request which no man can grant to the girl he loves—­and that is the request to keep away from her.  If Hilda did not want me, I wanted Hilda; and, being a man, I meant to find her.

My chances of discovering her whereabouts, however, I had to confess to myself (when it came to the point) were extremely slender.  She had vanished from my horizon, melted into space.  My sole hint of a clue consisted in the fact that the letter she sent me had been posted at Basingstoke.  Here, then, was my problem:  given an envelope with the Basingstoke postmark, to find in what part of Europe, Asia, Africa, or America the writer of it might be discovered.  It opened up a fine field for speculation.