After the hero Qi Rufeng raised Fang Gang (Wang Yu), the son of Fang Cheng, the servant who died to save him, he wanted to make him the head of the house, which attracted the jealousy of Fang Gang's senior brother. Qi Rufeng's daughter Qi Pei, who failed to pursue Fang Gang, joined her senior brother to compete with Fang Gang, but accidentally cut off Fang Gang's right arm, and Fang Gang was injured and fled from the Qi family. Fang Gang, who only had his left arm left, was depressed for a while after being rescued by the girl Xiaoman (Jiao Jiao), but finally regained his confidence with Xiaoman's encouragement, and practiced the "Left Hand Knife" stunt with the secret book "Left Hand Atlas" left by Xiaoman's father. Qi Rufeng's enemy, Smiling Erlang and the long-armed god and demon, killed all of Qi's disciples and imprisoned Qi Pei and Qi Rufeng. Taking into account the teacher's kindness, Fang Gang decided to help the Qi family regardless of his previous suspicions.