In late Ming Dynasty China, three sworn brothers, Shen Lian, Lu Jianxing, and Jin Yichuan, serve as elite members of the Imperial Assassins. Tasked with capturing the powerful eunuch Wei Zhongxian, who has fallen out of favor with the Emperor, they find themselves embroiled in a deadly conspiracy. Shen Lian, the most skilled and conflicted among them, hesitates when faced with an ethical dilemma during the mission. As they navigate betrayal and political intrigue, each brother is forced to confront his own personal demons and loyalties.

As they proceed with their mission, the brothers become entangled in a complex web of deceit and power struggles within the palace. Their bond is tested when hidden motives and past secrets come to light, leading to a series of tragic consequences. Opposing forces seek to exploit their vulnerabilities, pushing them to make unimaginable sacrifices. Amidst growing tensions and mounting danger, they must rely on each other's strengths to survive while grappling with their integrity and honor amid a treacherous era.