Jiang Feng and Yan Nantian become sworn brothers. Jiang Feng was injured during a misadventure and was rescued by the sisters Yaoyue and Lianxing of Yihua Palace. The sisters fall in love with Jiang Feng, but he spurns them because of their arrogance. Jiang Feng falls in love with the slave girl Hua Yuenu instead, and soon Hua becomes pregnant with his child.
Jiang Feng and Hua Yuenu manage to flee, but are tracked down by the sisters when Jiang's servant betrays them. Hua Yuenu gives birth to a pair of twin boys and dies together with Jiang Feng. As the ultimate vengeance for Jiang Feng's scorn, Yaoyue decides to make Jiang's sons kill each other. She raises one of the twins as her own child and names him "Hua Wuque". The other child is saved by Yan Nantian. Yan Nantian pursues Jiang Feng's treacherous servant into Villains' Valley to avenge his sworn brother, where he encounters the notorious Ten Great Villains, a group of the most brutal and malevolent criminals in the world. He is eventually overwhelmed and knocked out. Surprisingly, the villains do not harm the child, and instead intend to raise him as their student and "groom" him to become the greatest villain ever.
More than a decade later, the twins grow up into a pair of handsome youths. Yaoyue teaches Hua Wuque her formidable style of martial arts, and sends him to kill his brother without telling him about his origins. Concurrently, the other child Xiaoyu'er is trained by the Ten Great Villains in a variety of fighting styles, as well as many unique "villainous" skills such as poisons, theft, and disguise. Xiaoyu'er ventures into the jianghu (martial artists' community) alone, and his adventures lead him to encounters with many young maidens such as Tie Xinlan, Su Ying and Zhang Jing. He develops complex romantic relationships with most of them. Meanwhile Hua Wuque continues to pursue him, and the two clash on many occasions. Hua Wuque is superior to Xiaoyu'er in martial arts, but the latter usually manages to survive by using his wits and cunning.
Initially the twins are hostile towards one another, as their personalities are completely different; Hua Wuque is righteous and somewhat naive, while Xiaoyu'er is expedient and cunning. However the two eventually develop a grudging level of friendship and respect after being forced through a series of trials and adventures together. At the same time, they also become entangled in love triangles with several of the maidens they meet.
Yaoyue is determined to make the twins kill each other, and she forces Hua Wuque to challenge Xiaoyu'er to a fight to the death. Xiaoyu'er consumes some unidentified pills and is seemingly killed by Hua Wuque during the duel. After his apparent death, Yaoyue exposes her true intentions, as well as the history of the twins and her plan to make their father pay for betraying her love. Hua Wuque is shocked to hear the truth, but soon afterwards Xiaoyu'er comes back to life, revealing that he actually feigned death by consuming special drugs. The twins finally recognise and acknowledge each other as brothers.