Childhood friends Chen Ke Hai and Fang Li went their separate ways and reunited in Secret Service No. 76. In 1939, the Bureau of Investigation and Statistics created a special class to combat No. 76 of Wang Jing Wei's regime, hoping to resist Japan. Chen Ke Hai, now a secret member of the Communist Party, returns to Shanghai with the mission to infiltrate No. 76, where Fang Li is the leader. Brutal experiments reveal the truth about the bureau. Chen and Fang are separated after a failed assassination attempt. Faced with a drastically different Chen Ke Hai, Fang Li tests him and places an agent alongside him. Chen Ke Hai struggles to convey valuable information to his party without yielding. After the war, former colleagues have a final confrontation due to their contrasting beliefs.