“We had very definite proof,” continued Smith, “of the fact that Fu-Manchu and company were conversant with that elaborate system of secret rooms and passages which forms a veritable labyrinth, in, about, and beneath Graywater Park.  Some of the passages we explored.  That Sir Lionel should be ignorant of the system was not strange, considering that he had but recently inherited the property, and that the former owner, his kinsman, regarded the secret as lost.  A starting-point was discovered, however, in the old work on haunted manors unearthed in the library, as you remember.  There was a reference, in the chapter dealing with Graywater, so a certain monkish manuscript said to repose in the national collection and to contain a plan of these passages and stairways.

“The Keeper of the Manuscripts at the Museum very courteously assisted me in my inquiries, and the ancient parchment was placed in my hands.  Sure enough, it contained a carefully executed drawing of the hidden ways of Graywater, the work of a monk in the distant days when Graywater was a priory.  This monk, I may add—­a certain Brother Anselm—­ afterwards became Abbot of Graywater.”

“Very interesting!” cried sir Lionel loudly; “very interesting indeed.”

“I copied the plan,” resumed Smith, “with elaborate care.  That labor, unfortunately, was wasted, in part, at least.  Then, in order to confirm my suspicions on the point, I endeavored to ascertain if the monk’s MS. had been asked for at the Museum recently.  The Keeper of the Manuscripts could not recall that any student had handled the work, prior to my own visit, during the past ten years.

“This was disappointing, and I was tempted to conclude that Fu-Manchu had blundered on to the secret in some other way, when the Assistant Keeper of Manuscripts put in an appearance.  From him I obtained confirmation of my theory.  Three months ago a Greek gentleman—­possibly, Sir Lionel, your late butler, Homopoulo—­obtained permission to consult the MS., claiming to be engaged upon a paper for some review or another.

“At any rate, the fact was sufficient.  Quite evidently, a servant of Fu-Manchu had obtained a copy of the plan—­and this within a day or so of the death of Mr. Brangholme Burton—­whose heir, Sir Lionel, you were!  I became daily impressed anew with the omniscience, the incredible genius, of Dr. Fu-Manchu.

“The scheme which we know of to compass the death, or captivity, of our three selves and Karamaneh was put into operation, and failed.  But, with its failure, the utility of the secret chambers was by no means terminated.  The local legend, according to which a passage exists, linking Graywater and Monkswell, is confirmed by the monk’s plan.”

“What?” cried Sir Lionel, springing to his feet—­“a passage between the Park and the old tower!  My dear sir, it’s impossible!  Such a passage would have to pass under the River Starn!  It’s only a narrow stream, I know, but——­”