During the Zhenguan period, Chang'an, the capital of the Tang Dynasty, suffered from drought for several years, and the land was thousands of miles away. The people of the Li people prayed for rain every day, but they could not expect any rain. There was a man named Guiguzi, the Immortal Master, who decided that it would rain at 3:15 p.m. the next day, three o'clock in the city and seven o'clock outside the city. The golden horn old dragon who was in charge of the rain didn't believe it. He bet with the Immortal Master Guiguzi that he would go back to his house and open the storm book to check. The next day there was really rain. The book clearly wrote: clouds were set in the morning, thunder was running at the moment, it rained at noon, and the rain would stop soon. The raindrop is exactly what Guiguzi said. So he tampered with the Rain Book privately, changing the three o'clock in the city to seven o'clock, and the seven o'clock outside the city to three o'clock. As a result, heavy rain fell in the city, drowning many civilians, but only three points fell outside the city. The fields were still dry, the seedlings withered, and the crops were harvested. A loyal minister told the story to the Jade Emperor. The Jade Emperor was so angry that he decreed to behead the Golden Horn Dragon in public. Old Dragon in Golden Horn doesn't know well! Extremely frightened, Li Shimin immediately went to the palace to beg the Emperor of the Tang Dynasty Li Shimin to protect his life. Li Shimin thought that he was the founding father of the country and was gracious enough to avoid capital punishment. The next day Li Shimin designed to invite the Prime Minister Wei Zheng, who was executing the execution, to play chess in the palace. The execution time had come, and Wei Zheng had no plan to escape. Finally, he fell asleep at the table and dreamed of killing the golden horn dragon. In an instant, the bloody dragon head rolled into the palace.