Harry raised an eyebrow, but returned his hand to his lap. "No harm, huh?" he said, instilling calm into his voice. "Don't hear much of that from your kind." He frowned slightly, bottling up his fear. It took a moment, but Harry had spent a lifetime learning and perfecting emotional control, and within a minute, the fear had abated. He glanced again at the young man - certainly not so young as he appeared - and seemed to consider. After another long moment, he reached a conclusion and went for it.
"Truce? This conversation and for twenty-four hours hence?" A truce was always honored by the Old Ways, and was one of the most solemn of practices. Any who broke a truce could be immediately called upon for punishment through the Accords, but even beyond that, words had power. Someone who broke their word could injure their own power, and enough injury could cripple.
"I give my word and swear upon my power to abide by this truce, should you accept, and offer no violence nor threat of such." The language was archaic, probably unexpected from someone like Harry, but he was well accustomed to the uses and protocols of dealing with the supernatural.