Chen Gong serves as an adviser, initially aligning with Cao Cao during the coalition against Dong Zhuo. He aids Cao Cao's escape from Luoyang after Dong Zhuo seizes the Han court, motivated by Cao Cao's stated loyalty to the emperor. This partnership fractures during their journey when Cao Cao murders Lü Boshe and his family. Witnessing this act shatters Chen Gong's faith in Cao Cao's righteousness, prompting him to abandon Cao Cao quietly rather than kill him in his sleep.

Resurfacing later under Lü Bu, his defection occurs during Cao Cao's campaign against Tao Qian in Xu Province. Chen Gong collaborates with Zhang Miao to invite Lü Bu into Yan Province, enabling Lü Bu's seizure of Puyang and Juancheng. This betrayal exploits Cao Cao's absence to undermine his power base.

As Lü Bu's strategist, Chen Gong devises military plans, including the defense of Xiapi against Cao Cao's siege. He advises against Lü Bu's initial inclination to surrender and proposes tactical countermeasures to Cao Cao's maneuvers. When Lü Bu's subordinates capture Chen Gong and defect during the flooded siege of Xiapi, he faces Cao Cao.

Facing execution, Chen Gong refuses Cao Cao's offer to rejoin his forces. He invokes Cao Cao's past failures—the inability to kill Dong Zhuo and the murder of Lü Boshe—as proof of flawed character. Cao Cao honors Chen Gong's final request to care for his family before carrying out the execution. Anime portrayals within the film's narrative reflect these key events: his initial assistance to Cao Cao, disillusionment leading to defection, service under Lü Bu, and ultimate capture and execution following Xiapi's fall.