t verified it. I am now going to give myself an
intellectual treat."

"Wha-at?"

"I am going to prove practically whether my mind has grown rusty in the
last two years."

"I wish you'd say things so a plain man can understand 'em," grumbled the
other.

"You understand that we are in private room Number Seven, don't you? On the
other side of that wall is private room Number Six where a man has just
been shot. We know that, don't we? But the man who shot him was in _this_
room, the little hair-brushing old maid saw the pistol thrown from _this_
window, the dog found footprints coming from _this_ room, the murderer went
out through _that_ door into the alleyway and then into the street. He
couldn't have gone into the corridor because the door was locked on the
outside."

"He might have gone into the corridor and locked the door after him,"
objected Tignol.

Coquenil shook his head. "He could have locked the door after him on the
outside, not on the inside; but when we came in here, _it was locked on the
inside_. No, sir, that door to the corridor has not been used this
evening. The murderer bolted it on the inside when he entered from the
alleyway and it wasn't unbolted until I unbolted it myself."

"Then how, in Heaven's name----"

"Exactly! How could a man in this room kill a man in the next room? That is
the problem I have been working at for an hour. And I believe I have solved
it. Listen. Between these rooms is a solid wooden partition with no door in
it--no passageway of any kind. Yet the man in there is dead, we're sure of
that. The pistol was here, the bullet went there--somehow. _How_ did it go
there? _Think_."

The detective paused and looked fixedly at the wall near the heavy
sideboard. Tignol, half fascinated, stared at the same spot, and then, as a
new idea took form in his brain, he blurted out: "You mean it went _through
the wall?_"

"Is there any other way?"

The old man laid a perplexed forefinger along his illuminated nose. "But
there is no hole--through the wall," he muttered.

"There is either a hole or a miracle. And between the two, I conclude that
there _is_ a hole which we haven't found yet."

"It might be back of that sideboard," ventured the other doubtfully.

But M. Paul disagreed. "No man as clever as this fellow would have moved a
heavy piece covered with plates and glasses. Besides, if the sideboard had
been moved, there would be marks on the floor and there are none. Now you