There was a moment's silence, for Polly did not reply immediately, and he went on making impossible knots in his bit of string. Then she said quietly —

"I think that I agree with those English people who say that an English jury would have condemned her… . I have no doubt that she was guilty. She may not have committed that awful deed herself. Some one in the Charlotte Square house may have been her accomplice and killed and robbed Lady Donaldson while Edith Crawford waited outside for the jewels. David Graham left his godmother at 8.30 p.m. If the accomplice was one of the servants in the house, he or she would have had plenty of time for any amount of villainy, and Edith Crawford could have yet caught the 9.10 p.m. train from the Caledonian Station."

"Then who, in your opinion," he asked sarcastically, and cocking his funny birdlike head on one side, "tried to sell diamond earrings to Mr. Campbell, the jeweller?"

"Edith Crawford, of course," she retorted triumphantly; "he and his clerk both recognized her."

"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."

"Surely —— "

"Think of a curious nature, warped morally, as well as physically — do you know how those natures feel? A thousand times more strongly than the even, straight natures in everyday life. Then think of such a nature brought face to face with this awful problem.

"Do you think that such a nature would hesitate a moment before committing a crime to save the loved one from the consequences of that deed? Mind you, I don't assert for a moment that David Graham had any intention of murdering Lady Donaldson. Tremlett tells him that she seems strangely upset; he goes to her room and finds that she has discovered that she has been robbed. She naturally suspects Edith Crawford, recollects the incidents of the other night, and probably expresses her feelings to David Graham, and threatens immediate prosecution, scandal, what you will.

"I repeat it again, I dare say he had no wish to kill her. Probably he merely threatened to. A medical gentleman who spoke of sudden heart failure was no doubt right. Then imagine David Graham's remorse, his horror and his fears. The empty safe probably is the first object that suggested to him the grim tableau of robbery and murder, which he arranges in order to ensure his own safety.

"But remember one thing: no miscreant was seen to enter or leave the house surreptitiously; the murderer left no signs of entrance, and none of exit. An armed burglar would have left some trace — some one would have heard something. Then who locked and unlocked Lady Donaldson's door that night while she herself lay dead?

"Some one in the house, I tell you — some one who left no trace — some one against whom there could be no suspicion — some one who killed without apparently the slightest premeditation, and without the slightest motive. Think of it — I know I am right — and then tell me if I have at all enlisted your sympathies in the author of the Edinburgh Mystery."

He was gone. Polly looked again at the photo of David Graham. Did a crooked mind really dwell in that crooked body, and were there in the world such crimes that were great enough to be deemed sublime?