A swordsman uses a specialized weapon made from a deformed sword, the lethal hook, to fight an underworld clan to clear his family name and save the girl he loves in ancient China.

Jen, nicknamed Ah Dai, had been a rebellious child. He fled home the age of 16. A few years later, he became the driver of the leader of the Underworld, Mr. Lin. He was deeply moved by the kindness and care Mr. & Mrs. Lin showed him, grateful enough to do anything for them in return. Ah Dai observed the conflicts and struggle for privileges in the Underworld, and its strange interactions with the police.