Rosanna Spearman has stolen the Diamond.

I'll go in directly, and tell my aunt the turn things have taken." "Not just yet, if you please, sir," said a melancholy voice behind us.
We both turned about, and found ourselves face to face with Sergeant Cuff.
"Why not just yet ?" asked Mr.Franklin.
"Because, sir, if you tell her ladyship, her ladyship will tell Miss Verinder." "Suppose she does.

What then ?" Mr.Franklin said those words with a sudden heat and vehemence, as if the Sergeant had mortally offended him.
"Do you think it's wise, sir," said Sergeant Cuff, quietly, "to put such a question as that to me--at such a time as this ?" There was a moment's silence between them: Mr.Franklin walked close up to the Sergeant.

The two looked each other straight in the face.

Mr.
Franklin spoke first, dropping his voice as suddenly as he had raised it.
"I suppose you know, Mr.Cuff," he said, "that you are treading on delicate ground ?" "It isn't the first time, by a good many hundreds, that I find myself treading on delicate ground," answered the other, as immovable as ever.
"I am to understand that you forbid me to tell my aunt what has happened ?" "You are to understand, if you please, sir, that I throw up the case, if you tell Lady Verinder, or tell anybody, what has happened, until I give you leave." That settled it.