He stood still in surprise and listened.

There was no sound to be heard, not the grating of a lock, nor the tinkling of a bell, nor the fall of a footstep.
He did not pause long, for he made up his mind as to what he should do in the flash of a moment's intuition.

It was physically impossible that she should have disappeared into any one of the houses which had their entrances within the dark tunnel he had just traversed.

Apart from the presumptive impossibility of her being lodged in such a quarter, there was the self-evident fact that he must have heard the door opened and closed.

Secondly, she could not have turned to the right, for in that direction the street was straight and without any lateral exit, so that he must have seen her.