Xu Xi (Jet Li) was originally a cold-blooded killer in the mysterious killer organization Unit 701. Because he didn't want to be a murder tool anymore, he escaped from the organization and came to Hong Kong to become an ordinary library clerk. As a result, he met the policeman Shek SIR and became friends with him. Unexpectedly, Unit 701 suddenly appeared in Hong Kong to hunt down the gang leader. For a while, Shek SIR and the police were helpless. Seeing his friend in danger, Xu Xi stepped forward and became the Black Knight. The Black Knight made the leader of Unit 701, Xiong Ju (Long Gang), very angry, so he sent Xu Xi's old lover Ruolan to persuade the Black Knight to surrender, but was rejected by Xu Xi. As a result, all colleagues in the library except Tracy (Karen Mok) died. In order to protect Tracy, Xu Xi became the Black Knight again and took a tough attitude to take her away, but was rejected by Tracy, who didn't know that the Black Knight was her lover Xu Xi. Later, in the process of confronting Xiong Ju and others, Xu Xi gradually found the emotions she wanted from Tracy.