I was in the house two hours or more, questioning servants, examining
doors and windows, and, to be candid, my investigations told me little.
When I left Queen's Square I knew I had a complex affair to deal with,
and it was natural my thoughts should fly to the one man who might help
me. If I could only interest Christopher Quarles in the case!

I remember speaking casually of a well-known person once and being met
with the question: Who is he? It may be that some of you have never heard
of Christopher Quarles, professor of philosophy, and one of the most
astute crime investigators of this or any other time. It has been my
privilege to chronicle some of our adventures together, and his help has
been of infinite benefit to me. Without it, not only should I have failed
to elucidate some of those mysteries the solving of which have made me a
power in the detective force, but I should never have seen his
granddaughter, Zena, who is shortly to become my wife.

For some months past the professor had given me no assistance at all.
He would not be interested in my cases, and would not enter the empty
room in his house in Chelsea where we had had so many discussions. It
was a fad of his that he could think more clearly in this room, which
had only three chairs and an old writing table in it, yet perhaps I
ought not to call it a fad, remembering the results of some of our
consultations there.

Months ago we had investigated a curious case in which jewels had been
concealed in a wooden leg. The solution had brought us a considerable
reward, and upon receiving the money Quarles had declared he would
investigate no more crimes. He had kept his word, had locked up the empty
room, and although I think I had sorely tempted him to break his vow on
more than one occasion, I had never quite succeeded.