“It does, or did, pass under the River Starn!” said Nayland Smith coolly.  “That it is still practicable I do not assert; what interests me is the spot at which it terminates.”

He plunged his hand into the pocket of the light overcoat which he wore over the borrowed suit of pyjamas in which the kindly Dr. Hamilton had clothed him.  He was seeking his pipe!

“Have a cigar, Smith!” cried Sir Lionel, proffering his case—­“if you must smoke; although I think our medical friends frowning!”

Nayland Smith took a cigar, bit off the end, and lighted up.  He began to surround himself with odorous clouds, to his evident satisfaction.

“To resume,” he said; “the Spanish priest who was persecuted at Graywater in early Reformation days and whose tortured spirit is said to haunt the Park, held the secret of this passage, and of the subterranean chamber in Monkswell, to which it led.  His confession—­ which resulted in his death at the stake!—­enabled the commissioners to recover from his chamber a quantity of church ornaments.  For these facts I am indebted to the author of the work on haunted manors.

“Our inquiry at this point touches upon things sinister and incomprehensible.  In a word, although the passage and a part of the underground room are of unknown antiquity, it appears certain that they were improved and enlarged by one of the abbots of Monkswell—­at a date much later than Brother Anselm’s abbotship—­and the place was converted to a secret chapel——­”

“A secret chapel!” said Dr. Hamilton.

“Exactly.  This was at a time in English history when the horrible cult of Asmodeus spread from the Rhine monasteries and gained proselytes in many religious houses of England.  In this secret chapel, wretched Churchmen, seduced to the abominable views of the abbot, celebrated the Black Mass!”

“My God!” I whispered—­“small wonder that the place is reputed to be haunted!”

“Small wonder,” cried Nayland Smith, with all his old nervous vigor, “that Dr. Fu-Manchu selected it as an ideal retreat in times of danger!”

“What! the chapel?” roared Sir Lionel.

“Beyond doubt!  Well knowing the penalty of discovery, those old devil-worshipers had chosen a temple from which they could escape in an emergency.  There is a short stair from the chamber into the cave which, as you may know, exists in the cliff adjoining Monkswell.”

Smith’s eyes were blazing now, and he was on his feet, pacing the floor, an odd figure, with his bandaged skull and inadequate garments, biting on the already extinguished cigar as though it had been a pipe.

“Returning to our rooms, Petrie,” he went on rapidly, “who should I run into but Summers!  You remember Summers, the Suez Canal pilot whom you met at Ismailia two years ago?  He brought the yacht through the Canal, from Suez, on which I suspect Ki-Ming came to England.  She is a big boat—­used to be on the Port Said and Jaffa route before a wealthy Chinaman acquired her—­through an Egyptian agent—­for his personal use.