故事发生的背景是民国初期的上海，罗珊珊（甄锡饰）早年留学日本，她所学专业是犯罪鉴证。学成归来后，她进入巡捕房，成了有史以来的第一任女探长。其实罗珊珊选择学习犯罪鉴证并加入巡捕房，最重要的任务是为了查清五年前的一个悬案。五年前，珊珊的父亲罗成（侯长荣饰）无故失踪，从此杳无音讯。成为女探长后，巡捕房给珊珊安排了搭档——新任的探长刘梵希（欧阳震华饰），刘梵希曾经是罗成的徒弟，他一直没有放弃调查罗成的失踪案。罗珊珊整理东西时无意间发现罗成留下的一本记录，里面暗示五年前发生的断手案，幕后的策划人就是权势滔天的商会大佬许绍麟和现任巡捕房的督察长范德威（方子哥饰）。这两个人都是上海滩举足轻重的人物。此时，社会上又陆续出现新的断手案，罗珊珊和刘梵希必须要解开这些谜团，才能查出真相

The background of the story is Shanghai in the early Republic of China. Luo Shanshan (played by Zhen Xi) studied in Japan in her early years, and she majored in criminal forensics. After returning from her studies, she entered the police station and became the first female detective in history. In fact, Luo Shanshan chose to study criminal forensics and join the police station. The most important task was to investigate an unsolved case five years ago. Five years ago, Shanshan's father Luo Cheng (played by Hou Changrong) disappeared for no reason and has never been heard from since. After becoming a female detective, the patrol room arranged Shanshan's partner—the new detective Liu Fanxi (played by Ouyang Zhenhua). Liu Fanxi used to be Luo Cheng's apprentice, and he never gave up investigating Luo Cheng's disappearance. When Luo Shanshan was sorting out her things, she accidentally found a record left by Luo Cheng, which hinted that the murder case happened five years ago. . Both of these people are important figures in Shanghai. At this time, new cases of broken hands appeared one after another in the society. Luo Shanshan and Liu Fanxi had to unravel these mysteries in order to find out the truth