The knock was repeated, and this time it was given in a peculiar manner, as if it were a special signal.
An expression of relief came to the faces of the old man and the girl, but they seemed very much surprised.
“Who can it be?” Isa asked, doubtingly.
“It is the secret signal,” said the man with the gray hair.
“That is true, but who should come here to give the signal?”
“It must be all right.”
“Wait. I will go into the back room. If it is repeated, open the door. Should it be an enemy or enemies, give me time to get away. That’s all. Hold them from rushing into the back room.”
“We will do that,” declared Diamond.
In a moment Isa disappeared.
The knock was given for the third time, and the old man approached the door, which he slowly and deliberately opened.