In the occupied Shanghai in 1943, Shen Mobai, an underground member of the Chinese Communist Party code-named "Nightingale", lurked as the deputy director of the telecommunications department of the puppet government. When the Japanese army launched the "Phantom Project" in an attempt to forge Allied radio signals, he formed a secret team with military reunification agent Gu Qingshuang and Youth Gang disciple Chen Tieshan. When Shen Mobai deciphered the secret message, he discovered that his adoptive father was actually Sato Ichiro, the head of Japanese intelligence, and Gu Qingshuang's lover was the patriotic student who was accidentally killed by Shen three years ago. When the three parties were fighting for the code book in the basement of the drug store in the French Concession, Chen Tieshan used his body to detonate explosives to cover his companions, and Gu Qingshuang hid the microfilm in Shen Mobai's pocket watch before she died. In the end, Shen Mobai, with his dual identity torn apart, used the sound of the piano to convey the key information that reshaped the situation in the Pacific War, but he disappeared forever into the morning mist of the Huangpu River.
