I still remember how terrified we were that day, while we desperately waited to learn if you and Dumbledore had escaped.

What do you intend, with your chess game, Sirius? What do you hope to accomplish? I would advise you to think carefully about that, when you frame your response to Harry. Capturing the king, of course--but don't forget the pieces that might have to be sacrificed to accomplish that. Are you willing to have Harry be one of them? If not, be careful.