When I obeyed his summons I found him pacing excitedly up and down the central room, while the old soldier who guarded the premises stood with military stiffness in a corner.

“My dear Jackson,” he cried, “I am so delighted that you have come, for this is a most inexplicable business.”

“What has happened, then?”

He waved his hand towards the case which contained the breastplate.

“Look at it,” said he.

I did so, and could not restrain a cry of surprise.  The setting of the middle row of precious stones had been profaned in the same manner as the upper ones.  Of the twelve jewels eight had been now tampered with in this singular fashion.  The setting of the lower four was neat and smooth.  The others jagged and irregular.

“Have the stones been altered?” I asked.

“No, I am certain that these upper four are the same which the expert pronounced to be genuine, for I observed yesterday that little discoloration on the edge of the emerald.  Since they have not extracted the upper stones, there is no reason to think the lower have been transposed.  You say that you heard nothing, Simpson?”

“No, sir,” the commissionaire answered.  “But when I made my round after daylight I had a special look at these stones, and I saw at once that someone had been meddling with them.  Then I called you, sir, and told you.  I was backwards and forwards all night, and I never saw a soul or heard a sound.”

“Come up and have some breakfast with me,” said Mortimer, and he took me into his own chambers.—­“Now, what do you think of this, Jackson?” he asked.

“It is the most objectless, futile, idiotic business that ever I heard of.  It can only be the work of a monomaniac.”

“Can you put forward any theory?”

A curious idea came into my head.  “This object is a Jewish relic of great antiquity and sanctity,” said I.  “How about the anti-Semitic movement?  Could one conceive that a fanatic of that way of thinking might desecrate——­”

“No, no, no!” cried Mortimer.  “That will never do!  Such a man might push his lunacy to the length of destroying a Jewish relic, but why on earth should he nibble round every stone so carefully that he can only do four stones in a night?  We must have a better solution than that, and we must find it for ourselves, for I do not think that our inspector is likely to help us.  First of all, what do you think of Simpson, the porter?”

“Have you any reason to suspect him?”

“Only that he is the one person on the premises.”

“But why should he indulge in such wanton destruction?  Nothing has been taken away.  He has no motive.”

“Mania?”

“No, I will swear to his sanity.”

“Have you any other theory?”

“Well, yourself, for example.  You are not a somnambulist, by any chance?”

“Nothing of the sort, I assure you.”