“It is difficult to suggest anything more—­short of keeping your day watches all night.”

“We could not afford that.”

“At least, I should communicate with the police, and have a special constable put on outside in Belmore Street,” said I.  “As to the letter, if the writer wishes to be anonymous, I think he has a right to remain so.  We must trust to the future to show some reason for the curious course which he has adopted.”

So we dismissed the subject, but all that night after my return to my chambers I was puzzling my brain as to what possible motive Professor Andreas could have for writing an anonymous warning letter to his successor—­for that the writing was his was as certain to me as if I had seen him actually doing it.  He foresaw some danger to the collection.  Was it because he foresaw it that he abandoned his charge of it?  But if so, why should he hesitate to warn Mortimer in his own name?  I puzzled and puzzled until at last I fell into a troubled sleep, which carried me beyond my usual hour of rising.

I was aroused in a singular and effective method, for about nine o’clock my friend Mortimer rushed into my room with an expression of consternation upon his face.  He was usually one of the most tidy men of my acquaintance, but now his collar was undone at one end, his tie was flying, and his hat at the back of his head.  I read his whole story in his frantic eyes.

“The museum has been robbed!” I cried, springing up in bed.

“I fear so!  Those jewels!  The jewels of the urim and thummim!” he gasped, for he was out of breath with running.  “I’m going on to the police-station.  Come to the museum as soon as you can, Jackson!  Good-bye!” He rushed distractedly out of the room, and I heard him clatter down the stairs.

I was not long in following his directions, but I found when I arrived that he had already returned with a police inspector, and another elderly gentleman, who proved to be Mr. Purvis, one of the partners of Morson and Company, the well-known diamond merchants.  As an expert in stones he was always prepared to advise the police.  They were grouped round the case in which the breastplate of the Jewish priest had been exposed.  The plate had been taken out and laid upon the glass top of the case, and the three heads were bent over it.

“It is obvious that it has been tampered with,” said Mortimer.  “It caught my eye the moment that I passed through the room this morning.  I examined it yesterday evening, so that it is certain that this has happened during the night.”

It was, as he had said, obvious that someone had been at work upon it.  The settings of the uppermost row of four stones—­the carnelian, peridot, emerald, and ruby—­were rough and jagged as if someone had scraped all round them.  The stones were in their places, but the beautiful gold-work which we had admired only a few days before had been very clumsily pulled about.