Famous artist painting

Famous artist painting
The curtain will fall of itself and immediately leave a square of shadow where previously there had been a square of light. To do this, you need but stretch your hand out of the closet, I shall understand your signal perfectly."
"And then?"
"Then you will see me coming round the corner of the 'off-turning' gallery."
"What am I to do then?"
Famous artist painting
"You will immediately come towards me, behind the man; but I shall already be upon him, and shall have seen his face."
I attempted a feeble smile.
"Why do you smile? Well, you may smile while you have the chance, but I swear you'll have no time for that a few hours from now.
"And if the man escapes?"
Famous artist painting