"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? CHAPTER XVIII THE THEFT AT THE ENGLISH PROVIDENT BANK "That question of motive is a very difficult and complicated one at times," said the man in the corner, leisurely pulling off a huge pair of flaming dog-skin gloves from his meagre fingers. "I have known experienced criminal investigators declare, as an infallible axiom, that to find the person interested in the committal of the crime is to find the criminal. "Well, that may be so in most cases, but my experience has proved to me that there is one factor in this world of ours which is the mainspring of human actions, and that factor is human passions. For good or evil passions rule this poor humanity of ours. Remember, there are the women! French detectives, who are acknowledged masters in their craft, never proceed till after they have discovered the feminine element in a crime; whether in theft, murder, or fraud, according to their theory, there is always a woman.