During the Japanese occupation of Harbin, a covert resistance group disguised as a harmonica society uses music to transmit intelligence and fight back against enemy forces, enduring betrayal and sacrifices.
In 1937, Harbin was under Japanese colonial rule. The Japanese and puppet forces brutally suppressed anti-Japanese resistance. The Harbin Harmonica Society was actually an underground intelligence base of the Chinese Communist Party. Qin Na led its members, using performances as cover to secretly pass intelligence and carry out anti-Japanese struggles.