"The First Major Case" is a historical drama based on the first major anti-corruption case in the People's Republic of China. Set in 1951, the story follows counter-espionage officer Chen Huaibang, who uncovers the shocking corruption of Liu Qingshan, a former revolutionary hero turned corrupt official. Despite their past, Chen stays true to justice, bringing Liu and his accomplice Zhang Zishan to trial. The film highlights Chen's battle of wits with Liu, Zhang, and the enemy spy known as "Qingmang."