Episode 3 of "Good Boy" kicks off with Han-na's narrative, as she stands on the brink of another championship, poised to etch her name in record books. However, at a pivotal instant, her long mane breaks free, casting a distracting shadow over her concentration and causing her to lose her focus.
The scene transitions seamlessly to Dong-ju, who bumps into Ju-young at the customs office, ultimately stirring up a commotion that lands him in hot water. Back at the precinct, Dong-ju attempts to convey that Min Ju-young is the mastermind behind the hit-and-run incident, but his words fall flat without tangible evidence. Just then, Jong-hyeon strolls in, leading to a sparring match between the two, with Jong-hyeon emerging victorious and casually revealing his background in Taekwondo, honed since childhood.
As the officers are away, news breaks about Gyeong-il's arrest. Dong-ju pays a visit to his mother, who clings to the hope that her son will soon be freed once the genuine perpetrator is apprehended. This encounter sparks Dong-ju's determination to delve deeper into the imported car that Ju-young used on the fatal night.
Elsewhere, Jong-hyeon discovers that Gyeong-il's case has been reassigned to a new prosecutor—his own brother. Their exchanges reveal a strained relationship, brimming with underlying animosity.
Elsewhere, Dong-ju valiantly endeavors to persuade Gyeong-il to unveil the truth, yet his efforts fall on deaf ears. Meanwhile, in the shadows, Ju-young issues a chilling command to a prison guard, instructing him to eliminate Gyeong-il. The following morning, Dong-ju receives the devastating news of Gyeong-il's demise, cleverly disguised as a suicide, with the prison guard's watch discovered at the crime scene, further complicating matters. This tragedy strikes again, as Gyeong-il's mother severes all ties with Dong-ju, leaving him reeling in grief and anger.
Driven by a storm of rage, Dong-ju storms into Ju-young's presence, unleashing a fury of punches upon him. Steadfast in his defiance, Dong-ju refuses to comply with any of Ju-young's prior demands, now that the tables have turned.
Parallel to this, Han-na, having tendered her resignation, stumbles upon a watch resembling Ju-young's amidst her father's belongings—a revelation that her father too had once worn the badge of a policeman. Intrigued, she visits a pawn shop, where the proprietor reveals that the watch belongs to a limited edition, favored by a notorious and influential smuggler. However, the authenticity of her find remains uncertain.
When Ju-young disposes of the prison guard for his incompetence, which inadvertently led to Dong-ju's discovery, he becomes acutely aware that someone has been delving into his documents. Han-na emerges as a potential threat to his empire, casting a shadow of suspicion over her.
Back in his quarters, Dong-ju uncovers a surprising truth: Gyeong-il was not his brother, but a fierce competitor. Their rivalry culminated in a sparring match where Gyeong-il sustained injuries.
On another somber day, a real estate agent knocks on Han-na's door, revealing that her mother, an insurance agent struggling with debts, has listed her father's house for sale. This revelation unearths another layer of Han-na's past—her mother's preoccupation with fixing advertisements on the day of her championship, which inadvertently distracted her from her focus.
On that fateful day, Han-na was also grappling with a chronic illness. As she stumbled out of the police station, weakness overcame her, and it was only by sheer providence that Dong-ju caught her just before she fell. Meanwhile, Jong-hyeon discovered that someone had been delving into Han-na's personal records at the police station, stirring up a sense of unease.
After an heartfelt conversation with Han-na and receiving back the medal he had pawned, Dong-ju resumed his arduous task of copying the book—a necessary endeavor to thwart Ju-young's looming lawsuit. The following day, Han-na, strengthened by newfound resolve, withdrew her resignation, while Jong-hyeon stepped forward to join the team, determined to shield her from the escalating dangers lurking in the shadows.
Later that evening, Dong-ju took a bold step, breaking into the customs office to confront Ju-young face-to-face. His voice resonated with defiance as he warned Ju-young of his impending reckoning. With these intense moments, the episode drew to a cliffhanger, leaving viewers on the edge of their seats.
