“What do you mean exactly, Sowerby?” said Dunbar, taking out his fountain-pen and tapping his teeth with it.

“I mean,” said Sowerby, “that someone connected with the gang must have located the site of these vaults from some very old map or book.”

“I think you said that the Reverend Somebody-or-Other avers that they were a crypt?”

“He does; and when he pointed out to me the way the pillars were placed, as if to support the nave of a church, I felt disposed to agree with him.  The place where the golden dragon used to stand (it isn’t really gold, by the way!) would be under the central aisle, as it were; then there’s a kind of side aisle on the right and left and a large space at top and bottom.  The pillars are stone and of very early Norman pattern, and the last three or four steps leading down to the place appear to belong to the original structure.  I tell you it’s the crypt of some old forgotten Norman church or monastery chapel.”

“Most extraordinary!” muttered Dunbar.

“But I suppose it is possible enough.  Probably the church was burnt or destroyed in some other way; deposits of river mud would gradually cover up the remaining ruins; then in later times, when the banks of the Thames were properly attended to, the site of the place would be entirely forgotten, of course.  Most extraordinary!”

“That’s the reverend gentleman’s view, at any rate,” said Sowerby, “and he’s written three books on the subject of early Norman churches!  He even goes so far as to say that he has heard—­as a sort of legend—­of the existence of a very large Carmelite monastery, accommodating over two hundred brothers, which stood somewhere adjoining the Thames within the area now covered by Limehouse Causeway and Pennyfields.  There is a little turning not far from the wharf, known locally—­it does not appear upon any map—­as Prickler’s Lane; and my friend, the vicar, tells me that he has held the theory for a long time”—­Sowerby referred to his notebook with great solemnity—­“that this is a corruption of Pre-aux-Clerce Lane.”

“H’m!” said Dunbar; “very ingenious, at any rate.  Anything else?”

“Nothing much,” said Sowerby, scanning his notes, “that you don’t know already.  There was some very good stuff in the place—­Oriental ware and so on, a library of books which I’m told is unique, and a tremendous stock of opium and hashish.  It’s a perfect maze of doors and observation-traps.  There’s a small kitchen at the end, near the head of the tunnel—­which, by the way, could be used as a means of entrance and exit at low tide.  All the electric power came through the meter of Kan-Suh Concessions.”

“I see,” said Dunbar, reflectively, glancing at his watch; “in a word, we know everything except"...

“What’s that?” said Sowerby, looking up.

“The identity of Mr. King!” replied the inspector, reaching for his hat which lay upon the table.

Sowerby replaced his book in his pocket.