徐夕原本是神秘的无痛杀手组织701部队里的杀手，因为厌倦了打打杀杀刀口舔血的生活，他逃离组织来到香港做了名普普通通的图书管理员，从此在图书馆安静看书与世无争。徐夕来香港不久，结识了警局石探长并与之下棋谈心成为好友，他偶尔也从石探长那里听说一些犯罪案件。这段时间石探长焦头烂额，因为很多贩毒分子被突然灭口，警方却根本不知道是何人所为。直到最后一名贩毒组织的活口被警方抓捕，石探长等人发现活口胸腔内植入了定时炸弹。就在警方拆弹时，徐夕突然联系石探长让他千万不要剪断定时炸弹里的蓝线。原来徐夕就是黑侠，他在石探长手机里植入窃听器发现石探长有险情，因此不得不暴露身份。但此时以为时已晚，炸弹爆炸，石探长死里逃生。很快701部队浮出水面，近期的暗杀行动都是他们的手笔，他们的目的就是捣毁香港贩毒组织让美国贩毒集团占领这里的市场。组织头目代号队长的熊菊派徐夕旧情人若兰劝徐夕归顺回到组织，徐夕断然拒绝。熊菊恼羞成怒，一场对徐夕的报复行动疯狂展开…

Xu Xi was originally a killer in Unit 701 of the mysterious Painless Killer Organization. The organization came to Hong Kong and became an ordinary librarian, and since then, he has read quietly in the library without contending with the world. Not long after Xu Xi came to Hong Kong, he got acquainted with Inspector Shi of the police station and became good friends with Chess. He occasionally heard about some criminal cases from Inspector Shi. During this time, Inspector Shi was in a state of distress, because many drug traffickers were suddenly silenced, but the police didn't know who did it. Until the last living member of the drug trafficking organization was arrested by the police, Inspector Shi and others discovered that a time bomb was implanted in the living member's chest. When the police were dismantling the bomb, Xu Xi suddenly contacted Inspector Shi to ask him not to cut the blue line in the time bomb. It turns out that Xu Xi is a black man. He implanted a bug in Detective Shi's cell phone and found that Detective Shi was in danger, so he had to reveal his identity. But it was too late at this time, the bomb exploded, and Inspector Shi narrowly escaped death. Soon Unit 701 surfaced, and the recent assassinations were all their work. Their purpose was to destroy the Hong Kong drug trafficking organization and let the American drug trafficking group occupy the market here. The leader of the organization, Xiong Ju, code-named Captain, sent Xu Xi's old lover Ruo Lan to persuade Xu Xi to return to the organization, but Xu Xi flatly refused. Xiong Ju became angry from embarrassment, and a retaliation against Xu Xi started crazily..