After she had passed, the blotch trembled, as though the moving shadow had disturbed it. Neither the woman nor the Arab noted the strange phenomenon.
Hassan led the way to the door that opened on the circular staircase. The Arab snapped his fingers. The door opened.
The woman did not appear to be surprised. Evidently she was familiar with this place and its mechanical mysteries. She went up the staircase.
Hassan closed the door and returned to the laboratory.
Then, from a corner of the room, appeared that same blotch that had been in the hallway. It took the shape of a man’s shadow. It moved toward the door that led to the circular staircase.
It seemed to rise and became human in form. A man dressed in black stood before the door, his sable cloak and his turned-down hat concealing his identity.
The man snapped his fingers. There was no result. He moved closer to the door, and repeated the action.
Still the door did not respond.
The head of the figure bowed, as though the man were looking at his feet. Carefully, he chose a position, picking the exact spot where he stood. As he snapped his fingers for the third time, the man in black moved his left foot slightly forward.
The panel-like door slid back. The Shadow stepped through and closed the door behind him. A soft laugh came from beneath the hat.