They were once classmates and close like brothers who have embarked on completely different paths. As they meet again at the No. 76 secret service, is it a friend or is it a foe? In the year 1939, the Bureau of Investigation and Statistics established a special training class to combat the No. 76 secret service of the Wang Jing Wei regime. Childhood friends Chen Ke Hai and Fang Li join with the hopes of resisting Japan to save the country. However, their brutal experiences allow Chen Ke Hai to see through the true face of the bureau. After failing in their last assassination attempt, Chen and Fang are separated. Two years later, Chen Ke Hai, who has secretly become a member of the Communist Party, returns to Shanghai with a new mission to infiltrate No. 76. He is reunited with Fang Li, who is now the head of No. 76. Faced with Chen Ke Hai whose personality has changed dramatically compared to the past, Fang Li repeatedly tries to test him and even places a female agent by his side. Alone in the enemy camp, Chen Ke Hai does not cower as he fights to transmit valuable intel to his party. At the same time, his actions push Fang Li's suspicions to the brink. After the war against Japan, the pair of former classmates enter into a final showdown to uphold their contrasting beliefs.