“Yes,” says the Sergeant, as if he was actually reading my thoughts in the dark.  “Instead of putting me on the scent, it may console you to know, Mr. Betteredge (with your interest in Rosanna), that you have been the means of throwing me off.  What the girl has done, to-night, is clear enough, of course.  She has joined the two chains, and has fastened them to the hasp in the tin case.  She has sunk the case, in the water or in the quicksand.  She has made the loose end of the chain fast to some place under the rocks, known only to herself.  And she will leave the case secure at its anchorage till the present proceedings have come to an end; after which she can privately pull it up again out of its hiding-place, at her own leisure and convenience.  All perfectly plain, so far.  But,” says the Sergeant, with the first tone of impatience in his voice that I had heard yet, “the mystery is—­what the devil has she hidden in the tin case?”

I thought to myself, “The Moonstone!” But I only said to Sergeant Cuff, “Can’t you guess?”

“It’s not the Diamond,” says the Sergeant.  “The whole experience of my life is at fault, if Rosanna Spearman has got the Diamond.”

On hearing those words, the infernal detective-fever began, I suppose, to burn in me again.  At any rate, I forgot myself in the interest of guessing this new riddle.  I said rashly, “The stained dress!”

Sergeant Cuff stopped short in the dark, and laid his hand on my arm.

“Is anything thrown into that quicksand of yours, ever thrown up on the surface again?” he asked.

“Never,” I answered.  “Light or heavy whatever goes into the Shivering Sand is sucked down, and seen no more.”

“Does Rosanna Spearman know that?”

“She knows it as well as I do.”

“Then,” says the Sergeant, “what on earth has she got to do but to tie up a bit of stone in the stained dress and throw it into the quicksand?  There isn’t the shadow of a reason why she should have hidden it—­and yet she must have hidden it.  Query,” says the Sergeant, walking on again, “is the paint-stained dress a petticoat or a night-gown? or is it something else which there is a reason for preserving at any risk?  Mr. Betteredge, if nothing occurs to prevent it, I must go to Frizinghall to-morrow, and discover what she bought in the town, when she privately got the materials for making the substitute dress.  It’s a risk to leave the house, as things are now—­but it’s a worse risk still to stir another step in this matter in the dark.  Excuse my being a little out of temper; I’m degraded in my own estimation—­I have let Rosanna Spearman puzzle me.”

When we got back, the servants were at supper.  The first person we saw in the outer yard was the policeman whom Superintendent Seegrave had left at the Sergeant’s disposal.  The Sergeant asked if Rosanna Spearman had returned.  Yes.  When?  Nearly an hour since.  What had she done?  She had gone up-stairs to take off her bonnet and cloak—­and she was now at supper quietly with the rest.