We know, of course what had happened, but Jake did not.
He had come to the end of the log which Sam had thrown down to stop up the passage way, and there was really no way for him to go.

He supposed, of course, that he had somehow wandered out of his way, leaving the main alley and following a side one to its end.

He therefore retraced his steps, feeling, as he went, for an opening upon one side or the other.

He found several, but none of them did him any good.

Following each a little way he came to its end in the matted logs, and had to try again.