crossed the
street, walked along for a few paces, then paused at the curb and
looked back toward Hume's doorway. Then he returned with quick steps
and an alert look in his eyes.

"Now we'll go upstairs," he said.

But before doing so he stopped and examined the lock of the street
door closely; then he mounted the stairs slowly, his glances seeming
to take in everything. At the top he paused, his head bent, apparently
in deep thought. Then he lifted it suddenly, and laughed exultantly.

"That's it," he said, "I'm quite sure that is it."

"I wouldn't doubt your word for an instant," said Pendleton, in
something like his old voice. "Whatever it is, I'm quite sure it is if
you say so."

The policeman on guard in the hall examined them carefully.

"All right," said he, after they had explained and he had verified it
by calling to his mate at the street door. "Go right to work, gents.
I'm here to see that nobody gets in from above by way of the scuttle,
and I guess I won't be in the way."

There were three gas branches at intervals along the length of the dim
hall, each with a cluster of four jets. Ashton-Kirk lighted all three
of these and began making a careful examination of the passage. Along
toward the rear was a stairway leading to the floor above. Next this
was a small room in which there was a water tap. At the extreme end of
the hall was a window with a green shade drawn to the bottom.

Ashton-Kirk regarded this for a moment intently. Then he reached up
and turned off the gas at the branch nearest the window. Daylight
could now be seen through the blind; the investigator pointed and
said:

"This shows us something. About six inches of the bottom of the blind
is of a decidedly lighter color than the remainder. This is caused by
exposure to the light and indicates that this blind has seldom been
drawn in daylight as it is now."

He drew back the blind and looked at the side nearest the window. At
the top of the faded space was a heavy dark line.

"I'll modify that last statement," said he, with satisfaction. "I'll
go as far as to say, now, that the blind has never been drawn since it
was put up. This thick line marks the part that lay across the top of
the roller, and the dust seems never to have been disturbed."

The gas was lighted once more.

"Hume did not draw that curtain," said Ashton-Kirk, decidedly. "He
was too careless a man, apparently, to think of such a thing. The
intruders, whoever they we