Deception practised on Lord Cantlemere

Deception practised upon Lord Cantlemere by Sherlock Holmes.

“One moment, sir,” said he. “To actually go off with the Mazarin stone would be a more serious offence than to be found in temporary possession of it.”
“Sir, this is intolerable! Let me pass.”
“Put your hand in the right-hand pocket of your overcoat.”
“What do you mean, sir?”
“Come — come, do what I ask.”
An instant later the amazed peer was standing, blinking and stammering, with the great yellow stone on his shaking palm.
“What! What! How is this, Mr. Holmes?”
I took the liberty — the very great liberty, I admit — of putting the stone into your pocket at the beginning of our interview.”