Bad Boy is a drama about a guy, who changes his destiny in pursuit of power. Shim Gun Wook (Kim Nam Gil) plots revenge against the Haeshin Group, a large corporation to whom Hong Tae Sung (Kim Jae Wook) is the heir.
Moon Jae-In's existence is effectively reduced as her boyfriend's mother hands her a money envelope, telling her she's not suited for her son because she was born poor.
Shim Gun-Wook's painful childhood slowly begins to unveil itself through his flashbacks. He decides to orchestrate his Grand (and thrilling) Revenge.
Mo-Ne believes that Gun-Wook is sincere about his feelings for her, rather than her lying fiancé who has a girlfriend on the side. The tension rises to a dramatic and rebellious peak.
After an awkward conversation on how Mo Ne confessed to Gun Wook that she wanted to get married to him and not Mr. Um, Jae In was told the truth that Gun Wook was not Tae Sung Hong.
Two cops track down Tae Sung Choi (AKA Gun Wook) to the orphanage where he'd been sent after being rejected by the Hong's.
Jae In and Tae Sung find themselves stranded and at the mercy of one another.
The police are quickly beginning to places the puzzles pieces togther regarding Sun Young's death. This throws both Tae Sung and Gun Wook in a whirlwind of emotion, but neither are willing to show it.
With the help of his friend Gun Wook is able to catch the culprit behind the stolen materials.
The detectives confirm that the first Hong Tae Sung is still alive, and that he may be using an alias.