“The human heart is unsearchable,” I said gently.  “Who is to fathom it?”

“In other words, ma’am—­though he hadn’t the shadow of a reason for taking the Diamond—­he might have taken it, nevertheless, through natural depravity.  Very well.  Say he did.  Why the devil——­”

“I beg your pardon, Mr. Bruff.  If I hear the devil referred to in that manner, I must leave the room.”

“I beg your pardon, Miss Clack—­I’ll be more careful in my choice of language for the future.  All I meant to ask was this.  Why—­even supposing he did take the Diamond—­should Franklin Blake make himself the most prominent person in the house in trying to recover it?  You may tell me he cunningly did that to divert suspicion from himself.  I answer that he had no need to divert suspicion—­because nobody suspected him.  He first steals the Moonstone (without the slightest reason) through natural depravity; and he then acts a part, in relation to the loss of the jewel, which there is not the slightest necessity to act, and which leads to his mortally offending the young lady who would otherwise have married him.  That is the monstrous proposition which you are driven to assert, if you attempt to associate the disappearance of the Moonstone with Franklin Blake.  No, no, Miss Clack!  After what has passed here to-day, between us two, the dead-lock, in this case, is complete.  Rachel’s own innocence is (as her mother knows, and as I know) beyond a doubt.  Mr. Ablewhite’s innocence is equally certain—­or Rachel would never have testified to it.  And Franklin Blake’s innocence, as you have just seen, unanswerably asserts itself.  On the one hand, we are morally certain of all these things.  And, on the other hand, we are equally sure that somebody has brought the Moonstone to London, and that Mr. Luker, or his banker, is in private possession of it at this moment.  What is the use of my experience, what is the use of any person’s experience, in such a case as that?  It baffles me; it baffles you, it baffles everybody.”

No—­not everybody.  It had not baffled Sergeant Cuff.  I was about to mention this, with all possible mildness, and with every necessary protest against being supposed to cast a slur upon Rachel—­when the servant came in to say that the doctor had gone, and that my aunt was waiting to receive us.

This stopped the discussion.  Mr. Bruff collected his papers, looking a little exhausted by the demands which our conversation had made on him.  I took up my bag-full of precious publications, feeling as if I could have gone on talking for hours.  We proceeded in silence to Lady Verinder’s room.