Gu Yizhong, a scion of the Gu family in Suzhou, returns to China after completing his studies in the Architecture Department at the University of Pennsylvania. When the war breaks out, a failed rescue mission to assist his underground party girlfriend exposes all the contacts of the Suzhou underground organization. Falsely framed and accused by the Japanese collaborators, Gu Yizhong is mistaken for a traitor within the party. Unable to prove his innocence, he takes the initiative to infiltrate the Japanese collaborators and eventually becomes an undercover agent in the Suzhou special operations station of the Communist Party. Under immense pressure, Gu Yizhong confronts the station chief Zhou Zhifei and the Japanese advisor Kondo Tatsuo in a battle of wits. He seizes the opportunity to uncover the true traitor within the party, known as "Black Eight," and eliminates the threat. Continuously collecting secret intelligence for the Communist Party and saving fellow comrades in peril, Gu Yizhong provides significant support and assistance to the anti-Japanese cause of the Suzhou underground organization. With unwavering faith and courage, he grows constantly in the midst of struggle.