s. Either he has proved himself a dangerous revolutionary or he
has engineered the failure of a bank or chain of banks--"

"We can't prove it," I interrupted.

"No," said Foulet, "Neither can we. Neither can Scotland Yard--or the
secret services of Belgium or Germany or Italy or Spain. But there you
are--"

"You mean that in all these countries--?"

"I mean that for a year--probably longer--these countries have been
and are being steadily, and systematically, undermined. The morale of
the people is being weakened; their faith in their government is being
betrayed--and someone is behind it. Someone who can think faster and
plan more carefully than we--someone whose agents we always lose in
Constantinople! I'll wager you lost your man from a roof-top."

I nodded, my disgust at my own stupidity returning in full force.
"There was a lower roof and a maze of crisscross alleys," I muttered.
"He got away."

"Was there an airplane anywhere around?" asked Foulet.

I glanced at him in surprise. What good would an airplane have been on
a roof-top ten feet wide by twelve feet long? Then I remembered.
"There was an airplane," I said, "but it was a long way off, and I
could scarcely see it; but the air was very still and I heard the
motor."

Foulet nodded, "And if you had had a pair of glasses," he said gently,
"You would have seen that the airplane had a glider attached to it.
There is always an airplane--and a glider--when we lose our men from
the roofs of Constantinople."

"But that must be coincidence!" I insisted. "Why, I was on that roof
right on the fellow's heels--and the airplane was at least five miles
away!"

Foulet shrugged, "Coincidence--possibly," he said, "but it is our only
clue."

"Of course," I murmured thoughtfully, "you have never been able to
follow--"

Foulet smiled, "Can you imagine where that airplane would be by the
time we climbed down off our roofs and got to a flying field and
started in pursuit?"

* * * * *

We descended for dinner. Foulet's story had restored my
self-confidence somewhat--but I was still sore. Of course Foulet
connecting my vanishing man with that disappearing airplane was
absurd--but where had the man gone? Was my supposition that he had
jumped to a lower roof, climbed a wall and run through the maze of
alleyways in half a minute in any way less absurd?

We were halfway through dinner when Brice appeared. Brice was one of
the best men