Go first," he whispered.

The darkness was so complete that Garth had to keep his fingers on the
other's arm to avoid stumbling against the walls. Yet his guide went
with a quick assurance to the rear door which he opened with another
key. They stepped beneath a rough shelter of corrugated iron such as is
hastily thrown up for the protection in summer of washboards, or, in
winter, for the storing of wood. Black proceeded beneath this shelter
along the fence to the corner. Garth noticed a large accumulation of
rubbish in the yard, souvenirs, doubtless, of indolent and utilitarian
neighbors.

Black stooped. Evidently he had given a signal which Garth had not seen
or heard, for straightway he arose and leant against the fence, waiting.

"What now?" Garth asked.

Black raised his finger to his lips.

Garth looked down at a rustling among the rubbish. A thin piece of
flagging had opened at his feet as if hinged like a trap-door, leaving
visible the top of a flight of rough wooden steps.

Black stepped down and Garth followed. The steps led diagonally under
the angle of the fence. Others rose into the corner of the adjacent
yard. If this was their destination it was neither to one side nor
directly behind the empty house used as an entrance. Garth marvelled at
the simplicity of the contrivance. Two men in half a day could have
accomplished the entire excavation and arranged the steps. Moreover,
without a definite clue the police would never suspect such an entrance.

While Black carefully lowered the flag on the other side Garth glanced
around. They stood in the kitchen shed of a house which, of course,
faced the next street. Garth had no doubt that the place was masked with
a physician's office, or, perhaps, an appeal for boarders, who,
nevertheless, would always fail to find rooms available at the hour of
their application. He saw nothing of the man who had admitted them by
raising the flag. He was more disturbed than before, since he could
picture the inspector's bewilderment on learning that he had entered the
house which had been so recently raided and combed.

Garth had small time for speculation. He saw Black press an electric
button. Faintly he heard the response from a muffled bell--two rings
short, and one long. Almost at once the door opened a crack, but no
gleam of light came through. Black muttered something unintelligible to
Garth, and led him into a darkness as complete as that which had
oppressed him