The narrow passage was paved with brick, and this prevented Matt from seeing the tracks which an automobile might have left on the surface of bare ground.
Slowly the boys walked along the alley, peering at the doors on left and right as they advanced. They were about half-way through the alley when they found what they were seeking, namely, a wide door at the foot of a steep incline. The descent was not more than two feet downward from the surface of the alley, and the wide door was set well back, so that the cut-out place would not interfere with teaming through the passage.
"Py shinks," whispered Carl excitedly, "ve haf foundt der blace!"
"No doubt of it," answered Matt with a grim feeling of satisfaction.
There were no windows in the basement wall of the building, and those in the upper stories were dusty and cobwebbed.
Softly Matt descended to the door at the foot of the incline and motioned for Carl to follow.
The Dutch boy gained his side.
"Now rap," said Matt, "and see how good an imitation you can give of what you heard last night."
Carl drummed the peculiar tattoo. There was no response. After waiting a little he drummed it again, but louder.
This, somewhat unexpectedly, brought an answer.