Kang Benshan and Wang Ranqiu are workers at the Changxindian Railway Factory, having grown up in the “mouth” and “seam” areas at the heart of the ancient town of Changxindian in southwest Beijing. As skilled craftsmen, they tackle the toughest machine repairs and help build some of the finest trains.
Set in 1930s Shanghai, the drama follows Ma Tianming, a cunning conman who becomes entangled in a dangerous political conflict. After a twist of fate makes him a suspect in a case, he assumes the identity of Hengshan Hospital’s chief doctor, Cai Likun—only to discover that Cai is a member of the underground Communist Party. As he struggles to maintain his cover, Ma Tianming finds himself caught between survival and a greater cause.
Hua Long, Su Mei, Bao Zhan and Professor Liang comprise the SIG (Special Investigation Group). This group deals with the extremely abnormal and twisted investigations of homicide cases that are difficult to crack. In the process of solving the cases, each member must face their own dangers, conspiracy and growth.