"What makes you think so?"
"Look up there. What do you see?"
"Why, the coal-hole and its iron cover."
"Is the cover fastened over the hole?"
"Certainly."
"If any one has gone out by that way lately could they have fastened down the cover after them as we see it now?"
"Of course not."
"If any one expects to visit the great vault to-night, for instance, could they do so by way of this coal-hole?"
"Certainly not."
"Then isn't it evident that there must be some other way to reach the sub-cellar known to the frequenters of the vault?"