he method was no doubt suggested to Clay's ingenious mind by
the color of his accomplice's hair. The four pounds a week was a lure
which must draw him, and what was it to them, who were playing for
thousands? They put in the advertisement, one rogue has the temporary
office, the other rogue incites the man to apply for it, and together
they manage to secure his absence every morning in the week. From the
time that I heard of the assistant having come for half wages, it was
obvious to me that he had some strong motive for securing the
situation."

"But how could you guess what the motive was?"

"Had there been women in the house, I should have suspected a mere
vulgar intrigue. That, however, was out of the question. The man's
business was a small one, and there was nothing in his house which
could account for such elaborate preparations, and such an expenditure
as they were at. It must then be something out of the house. What could
it be? I thought of the assistant's fondness for photography, and his
trick of vanishing into the cellar. The cellar? There was the end of
this tangled clew. Then I made inquiries as to this mysterious
assistant, and found that I had to deal with one of the coolest and most
daring criminals in London. He was doing something in the
cellar--something which took many hours a day for months on end. What
could it be, once more? I could think of nothing save that he was
running a tunnel to some other building.

"So far I had got when we went to visit the scene of action. I surprised
you by beating upon the pavement with my stick. I was ascertaining
whether the cellar stretched out in front or behind. It was not in
front. Then I rang the bell, and, as I hoped, the assistant answered it.
We have had some skirmishes, but we had never set eyes upon each other
before. I hardly looked at his face. His knees were what I wished to
see. You must yourself have remarked how worn, wrinkled, and stained
they were. They spoke of those hours of burrowing. The only remaining
point was what they were burrowing for. I walked round the corner, saw
that the City and Suburban Bank abutted on our friend's premises, and
felt that I had solved my problem. When you drove home after the concert
I called upon Scotland Yard, and upon the chairman of the bank
directors, with the result that you have seen."

"And how could you tell that they would make their attempt to-night?" I
asked.

"Well, when they closed their League