A bloody bank robbery broke out in An City. The robbers' tactics were professional and cruel, and they seemed to have insight into the police's deployment. Ling Feng, deputy captain of criminal investigation, is a rising star in the police world. He believes in procedural justice and takes orders in times of danger. He calmly pursued the case, but met the mysterious man Shen Yan near the crime scene - a former elite special police officer who was expelled due to a tragic failure. Now his identity is a mystery, he acts ruthlessly, and he walks in a gray area.
Shen Yan is also tracking the robbers. His purpose is unknown, but his methods are on the edge of the law. When the two met for the first time, sparks flew: Ling Feng regarded him as a hidden danger that disrupted order; Shen Yan mocked him for being rigid and conservative and unable to get to the core of the truth. As the investigation deepened, the robbery actually involved the huge criminal organization "Dark River", and was closely related to the old case that caused Shen Yan to fall into the abyss.
Forced to form a subtle "cooperation": Ling Feng is in the light, using the police badge and rules as a shield; Shen Yan is in the dark, using intuition and iron-blood as the blade. A fierce collision of ideas - can procedural justice confront the deep-rooted darkness? What is the cost of a result-oriented extraordinary means?
When Ling Feng's dependent sister was in danger because the investigation touched the "underdark river", and when the mysterious connection between Shen Yan and the top leaders of the organization surfaced, trust was crumbling. In the end, the "Dark River" conspiracy to destroy the city came to light. Shen Yan is determined to use his body as bait and both will be destroyed; Ling Feng faces the cruelest choice in his career: Should he stick to the rules and sit back and watch the disaster, or should he break the iron law and dance in the abyss with the "scavenger" in the shadows?
The guardian of procedural justice and the scavenger who puts the results above all else will engage in an ultimate showdown involving life and death, faith and redemption atop the huge undercurrent of sin. Above the undercurrent, who is guarding the real light?
Purpose: justice