Strange Cause of Death

Jiang Chuan had just let his guard down when he remembered that Zhang Ling's father had recently passed away. He asked Su Zhen, "Do you know how Old Master Zhang died?"

Half-asleep, Su Zhen frowned upon hearing the question. After gathering his thoughts, he said, "It's not very clear. When I visited the mountain to see Old Master Zhang, he was alive and well. But a week later, when I visited again, he was gone. The Zhang family claims that he got drunk and fell off the mountain. But he walked that mountain path daily, and it wasn't his first time getting drunk. Why did he happen to fall this time?"