In 1988, Interpol Wei Guoping (translated by Zhang) witnessed the sacrifice of his comrade-in-arms in the pursuit of serial riddles, but the murderer escaped, which became the knot of Wei Guoping's heart. Eight years later, an appalling murder occurred in Ningjiang City, when Wei Guoping has grown into a mature captain of the criminal police. In the process of leading his team to investigate, he cracked a number of related cases one after another, but the murder was always full of doubts, and many clues were related to the serial riddle eight years ago. These discoveries excited Wei Guoping, but also became an obstacle for him to judge the case later. In the course of the case, a huge criminal syndicate gradually surfaced.

1988年，刑警衛國平（張譯 飾）在追捕連環謎案的行動中目睹戰友犧牲，而凶手卻逃跑了，此事成為衛國平的心結。八年後，寧江市發生了駭人聽聞的凶殺案，此時衛國平已成長為成熟的刑警隊長。他在帶領隊員調查的過程中相繼破獲了不少相關案件，但是凶殺案始終充滿疑雲，並且很多線索與八年前的連環謎案有關，這些發現讓衛國平振奮但也成為他後來判斷案情的阻礙。在案件的推進過程中，一個龐大的犯罪集團逐漸浮出水面……