“Evidently,” said Dunbar, resting his chin on the palms of his hands and his elbows upon the table.

“The office and warehouse staff of the ginger importing concern are innocent enough, as you know already.  Kan-Suh Concessions was conducted merely as a blind, of course, but it enabled the Chinaman, Ho-Pin, to appear in Wharf-end Lane at all times of the day and night without exciting suspicion.  He was supposed to be the manager, of course.  The presence of the wharf is sufficient to explain how they managed to build the place without exciting suspicion.  They probably had all the material landed there labeled as preserved ginger, and they would take it down below at night, long after the office and warehouse staff of Concessions had gone home.  The workmen probably came and went by way of the river, also, commencing work after nightfall and going away before business commenced in the morning.”

“It beats me,” said Dunbar, reflectively, “how masons, plumbers, decorators, and all the other artisans necessary for a job of that description, could have been kept quiet.”

“Foreigners!” said Sowerby triumphantly.  “I’ll undertake to say there wasn’t an Englishman on the job.  The whole of the gang was probably imported from abroad somewhere, boarded and lodged during the day-time in the neighborhood of Limehouse, and watched by Mr. Ho-Pin or somebody else until the job was finished; then shipped back home again.  It’s easily done if money is no object.”

“That’s right enough,” agreed Dunbar; “I have no doubt you’ve hit upon the truth.  But now that the place has been dismantled, what does it look like?  I haven’t had time to come down myself, but I intend to do so before it’s closed up.”

“Well,” said Sowerby, turning over a page of his notebook, “it looks like a series of vaults, and the Rev. Mr. Firmingham, a local vicar whom I got to inspect it this morning, assures me, positively, that it’s a crypt.”

“A crypt!” exclaimed Dunbar, fixing his eyes upon his subordinate.

“A crypt—­exactly.  A firm dealing in grease occupied the warehouse before Kan-Suh Concessions rented it, and they never seem to have suspected that the place possessed any cellars.  The actual owner of the property, Sir James Crozel, an ex-Lord Mayor, who is also ground landlord of the big works on the other side of the lane, had no more idea than the man in the moon that there were any cellars beneath the place.  You see the vaults are below the present level of the Thames at high tide; that’s why nobody ever suspected their existence.  Also, an examination of the bare walls—­now stripped—­shows that they were pretty well filled up to the top with ancient debris, to within a few years ago, at any rate.”

“You mean that our Chinese friends excavated them?”

“No doubt about it.  They were every bit of twenty feet below the present street level, and, being right on the bank of the Thames, nobody would have thought of looking for them unless he knew they were there.”