“When did she try to sell them the earrings?”

“Ah, that is what I cannot quite make out, and there to my mind lies the only mystery in this case.  On the 25th she was certainly in London, and it is not very likely that she would go back to Edinburgh in order to dispose of the jewels there, where they could most easily be traced.”

“Not very likely, certainly,” he assented drily.

“And,” added the young girl, “on the day before she left for London, Lady Donaldson was alive.”

“And pray,” he said suddenly, as with comic complacency he surveyed a beautiful knot he had just twisted up between his long fingers, “what has that fact got to do with it?”

“But it has everything to do with it!” she retorted.

“Ah, there you go,” he sighed with comic emphasis.  “My teachings don’t seem to have improved your powers of reasoning.  You are as bad as the police.  Lady Donaldson has been robbed and murdered, and you immediately argue that she was robbed and murdered by the same person.”

“But—­” argued Polly.

“There is no but,” he said, getting more and more excited.  “See how simple it is.  Edith Crawford wears the diamonds one night, then she brings them back to Lady Donaldson’s room.  Remember the maid’s statement:  ’My lady said:  “Have you put them back, my dear?”—­a simple statement, utterly ignored by the prosecution.  But what did it mean?  That Lady Donaldson could not see for herself whether Edith Crawford had put back the jewels or not, since she asked the question.”

“Then you argue—­”

“I never argue,” he interrupted excitedly; “I state undeniable facts.  Edith Crawford, who wanted to steal the jewels, took them then and there, when she had the opportunity.  Why in the world should she have waited?  Lady Donaldson was in bed, and Tremlett, the maid, had gone.

“The next day—­namely, the 25th—­she tries to dispose of a pair of earrings to Mr. Campbell; she fails, and decides to go to London, where she has a better chance.  Sir James Fenwick did not think it desirable to bring forward witnesses to prove what I have since ascertained is a fact, namely, that on the 27th of October, three days before her arrest, Miss Crawford crossed over to Belgium, and came back to London the next day.  In Belgium, no doubt, Lady Donaldson’s diamonds, taken out of their settings, calmly repose at this moment, while the money derived from their sale is safely deposited in a Belgian bank.”

“But then, who murdered Lady Donaldson, and why?” gasped Polly.

“Cannot you guess?” he queried blandly.  “Have I not placed the case clearly enough before you?  To me it seems so simple.  It was a daring, brutal murder, remember.  Think of one who, not being the thief himself, would, nevertheless, have the strongest of all motives to shield the thief from the consequences of her own misdeed:  aye! and the power too—­since it would be absolutely illogical, nay, impossible, that he should be an accomplice.”