t was opened the code was gone."

"You had had no occasion to go to the safe in the meantime?"

"None at all. I locked it at 10.20, and I unlocked it two hours later,
and that was all."

"You were not in the room the whole of the time, of course?"

"Oh, no. I have told you that at 10.20 I went to the Controller's room,
and after that I went out two or three times on one occasion or another.
But each time I locked the door of the room."

"Oh, you did? That is important. And you took all your keys with you, I
presume?"

"Yes, all. The keys on the bunch I took in my pocket, of course, and the
room door key I also took. There are one or two rather important papers
on my desk, you see, and anybody from the corridor might come in if the
door were left unlocked."

"The lock of the door would be a good deal easier to pick than that of
the safe," Hewitt observed, after examining it. "But that would be of no
great use with the safe locked. Shortly, then, the facts are these. You
locked the code safely away at 10.20, you left the room two or three
times, but each time the door, as well as the safe, was locked, and the
keys in your pocket; and then, at 12.20, or two hours exactly after the
code had been put safely away, you opened the safe again in presence of
the Controller's secretary, and the code had vanished. That is the whole
matter in brief, I take it?"

"Precisely." Mr. Telfer was pallid and bewildered. "It seems a total
impossibility," he said; "a total, absolute, physical impossibility; but
there it is."

"But as no such thing as a physical impossibility ever happens," Hewitt
replied calmly, "we must look further. Now, are there any other ways
into this room than by that door into the corridor? I see another door
here. What is that?"

"That door has been locked for ages. The room on the other side is one
like this, with a door in the corridor; it is used chiefly to store old
documents of no great importance, and I believe that whole stacks of
them, in bundles, are piled against the other side of that same door. We
will send for the key and see, if you like."

The key was sent for, and the door from the corridor opened. As Telfer
had led us to expect, the place was full of old papers in bundles and
parcels, thick with ancient dust, and these things were piled high
against the door next his room, and plainly had not been disturbed for
months, or even years.

"There remains the skylight," said Hewitt, "for I p