“One of the dwarfs—­”

“Not even one of the dwarfs,” said Bristol, “could have passed between those iron bars!”

“But there was blood on the window!”

“I know there was, and human blood.  It’s been examined!”

He stared at me fixedly.  The thing was unspeakably uncanny.

“To-night,” he went on, “I am remaining in here”—­nodding toward the Assyrian Room—­“and I have so arranged it that no mortal being can possibly know I am here.  Mostyn is staying, and you can stay, too, if you care to.  Owing to Professor Deeping’s will you are badly involved in the beastly business, and I have no doubt you are keen to see it through.”

“I am,” I admitted, “and the end I look for and hope for is the recovery of the slipper by its murderous owners!”

“I am with you,” said Bristol.  “It’s just a point of honour; but I should be glad to make them a present of it.  We’re ostentatiously placing a constable on duty in the hallway to-night—­largely as a blind.  It will appear that we’re taking no other additional precautions.”

He hurried off to make arrangements for my joining him in his watch, and thus again I lost my opportunity of confiding in him regarding the mysterious girl.

I half anticipated, though I cannot imagine why, that Earl Dexter would put in an appearance, during the day.  He did not do so, however, for Bristol had put a constable on the door who was well acquainted with the appearance of The Stetson Man.  The inspector, in the course of his investigations, had come upon what might have been a clue, but what was at best a confusing one.  Close by the wall of the curator’s house and lying on the gravel path he had found a part of a gold cuff link.  It was of American manufacture.

Upon such slender evidence we could not justly assume that it pointed to the presence of Dexter on the night of the attempted robbery, but it served to complicate a matter already sufficiently involved.

In pursuance of Bristol’s plan, I concealed myself that evening just before the closing of the Museum doors, in a recess behind a heavy piece of Babylonian sculpture.  Bristol was similarly concealed in another part of the room, and Mostyn joined us later.

The Museum was closed; and so far as evidence went the authorities had relied again upon the bolts and bars hitherto considered impregnable, and upon the constable in the hall.  The broken window was mended, the cut blind replaced, and within, in its shattered case, reposed the slipper of the Prophet.

All the blinds being lowered, the Assyrian Room was a place of gloom, yellowed on the western side by the moonlight through the blind.  The door communicating with the Burton Room was closed but not fastened.

“They operated last night,” Bristol whispered to me, “at the exact time when the moonlight shone through the hole in the westerly blind on to the case.  If they come to-night, and I am quite expecting them, they will have to dispense with that assistance; but they know by experience where to reach the case.”