“Birds of a feather—­” I suggested.

“But they are not birds of a feather!” cried Bristol.  “On your own showing, Hassan of Aleppo is simply waiting his opportunity to balance Dexter’s account forever!  I always knew Dexter was a clever man; I begin to think he’s the most daring genius alive!”

We mounted the steps of the Museum.  In the hallway Mostyn, the curator, awaited us.  Having greeted Bristol and myself he led the way to his private office, and from a pigeon-hole in his desk took out a letter typewritten upon a sheet of quarto paper.

Bristol spread it out upon the blotting pad and we bent over it curiously.

Sir—­

I believe I can supply information concerning the whereabouts of the missing slipper of Mohammed.  As any inquiry of this nature must be extremely perilous to the inquirer and as the relic is a priceless one, my fee would be 10,000 pounds.  The fanatics who seek to restore the slipper to the East must not know of any negotiations, therefore I omit my address, but will communicate further if you care to insert instructions in the agony column of Times.

Faithfully,
Earl Dexter

Bristol laughed grimly.

“It’s a daring game,” he said; “a piece of barefaced impudence quite characteristic.

“He’s posing as a sort of private detective now, and is prepared for a trifling consideration to return the slipper which he stole himself!  He must know, though, that we have his severed hand at the Yard to be used in evidence against him.”

“Is the Burton Room open to the public again?” I asked Mostyn.

“It is open, yes,” he replied, “and a quite unusual number of visitors come daily to gaze at the empty case which once held the slipper of the Prophet.”

“Has the case been mended?”

“Yes; it is quite intact again; only the exhibit is missing.”

We ascended the stairs, passed along the Assyrian Room, which seemed to be unusually crowded, and entered the lofty apartment known as the Burton Room.  The sunblinds were drawn, and a sort of dim, religious light prevailed therein.  A group of visitors stood around an empty case at the farther end of the apartment.

“You see,” said Mostyn, pointing, “that empty case has a greater attraction than all the other full ones!”

But I scarcely heeded his words, for I was intently watching the movements of one of the group about the empty case.  I have said that the room was but dimly illuminated, and this fact, together no doubt with some effect of reflected light, enhanced by my imagination, perhaps produced the phenomenon which was occasioning me so much amazement.

Remember that my mind was filled with memories of weird things, that I often found myself thinking of that mystic light which Hassan of Aleppo had called the light of El-Medineh—­that light whereby, undeterred by distance, he claimed to be able to trace the whereabouts of any of the relics of the Prophet.