To Calm the Troubled Times, I Have Hundreds of Millions of Poisons

This is a historical fantasy novel set during the Great Split of the Five Dynasties and Ten Kingdoms. The protagonist, Tang Li, has practiced medicine with his father since he was a child. A flood swept away his family. Later, it was discovered that the man-made disaster was caused by the methods of wizards recruited by Dongchuan Jiedushi Gu Yanhui. Fortunately, with the help of his friend's aunt, the protagonist joins the Shu clan, becomes a handyman disciple, and begins to practice dangerous poisonous skills, embarking on the road of painstaking revenge. If you want to take revenge on the evil people in troubled times, you have to be hundreds of millions more poisonous than the evil people. Destroy the heroes and bring peace to the troubled times. You are ruthless and just, and you are cunning and innocent. Let's see how I can quell the bandits, dominate the world with poison, and calm this troubled world?