I detected a doubtful point in his words. "How do you know that the second victim died of gas poisoning?" I asked.

The old man pointed to the drawing and grinned, "The picture says everything!"

As it turned out, the wavy lines Bingxin had drawn hinted that the room was filled with some sort of gas. "Besides, this killing mechanism must offer the victim a small chance of escaping,” explained the old man. “Otherwise, who would be willing to mutilate themselves? Since it’s a secret room, if I were the mastermind, I would certainly fill it with poisonous gas."

"You seem to know the ropes!" I remarked.

"I know a little," the old man modestly replied.

He grabbed a cigarette from Wang Yuanchao's cigarette case, slid it between his lips and leaned in so Wang Yuanchao could light the cigarette. From the look in Wang Yuanchao’s eyes, I recognized his impatience. Facing such a presumptuous...