The premiere episode of "Good Boy" unfurls with Dong-ju's poignant narration, painting a vivid picture of his former glory as a boxing champion, a title he once held dear until it was stripped away. Transitioning to the present, Dong-ju is now a humbled member of the police force, having suffered a demotion and resorting to selling his cherished gold medal for much-needed cash.
In parallel, Ji Han-na, the shooting prodigy, finds herself underappreciated and sidelined, used merely as a visual representation for the police rather than being actively engaged in duty. This revelation underscores a disturbing trend of discrimination against athletes within the force, who, having gained entry via a fast track rather than the conventional route of rigorous examinations and training, are met with prejudice.
Dong-ju's former mentor, Ko Man-sik, finds himself tasked with aiding in the apprehension of a notorious gang ring. Amidst the tense operation, Ko Man-sik briefly steps away to relieve himself, leaving Dong-ju to keep vigilant watch on the streets. However, a sudden, thunderous explosion shatters the silence, alerting the gang members to their impending peril and prompting their swift escape.
Dong-ju comes into direct confrontation with the elusive target, known as Golden Bunny, but fate is unkind as he is struck and rendered unconscious. The operation falls apart, leading to a dressing down for both Man-sik and Dong-ju by their peers.
Enter Shin Jae-hong, a former colleague of Dong-ju's, now serving as a traffic cop. Additionally, Dong-ju reconnects with Han-na, and their shared history bubbles to the surface as Dong-ju cheerfully confesses his enduring affection for her.
Simultaneously, Jong-hyeon, another athlete from their past, makes his presence known to Han-na. Subtle hints of a romantic entanglement between them emerge. Jong-hyeon, who has ascended to the position of an audit officer at the police station, is revealed to be the most career-successful among the athletes. However, his integrity and willingness to expose corrupt officers and pursue promotions have made him a pariah among his peers.
Meanwhile, Man-sik leaves Dong-ju to man a stakeout all alone. Later that fateful night, Dong-ju's derriere is unexpectedly struck by a speeding car. As the unidentified driver hastily speeds away, Dong-ju's hand becomes trapped in the window, causing him grievous harm. Upon his return, he discovers thieves in the act of siphoning fuel from Man-sik's car and making a swift getaway with it. A short distance further down the road, Dong-ju encounters a hit-and-run victim and rushes him to the hospital.
Subsequently, Dong-ju attempts to reach out to his brother but meets with no response. He attends a ceremony honoring his former coach, where he learns of a shocking revelation – the coach had maliciously spread rumors that Dong-ju's gold medal was the result of doping. This malicious act stemmed from Dong-ju's refusal to participate in MMA. Furthermore, there are hints that the coach influenced Dong-ju's brother to indulge in drugs, leading to his brother's mysterious disappearance.
The following day, Dong-ju is determined to uncover the perpetrator behind the hit-and-run incident. Recalling a report about a smuggled car, he breaks into the audit room and pilfers a crucial paper from a case file. To his astonishment, it turns out to be the very same car that had collided with him and was involved in the hit-and-run.
Concurrently, Jong-hyeon, who has been diligently probing the explosion during the failed undercover police operation, discovers that the hit-and-run victim had reported an arson just five minutes prior to the explosion. He shares this crucial piece of information with Man-sik, and they both concur that someone within their own ranks had leaked details about the operation. Jong-hyeon also realizes that Dong-ju might be in grave danger.
Dong-ju, acting on a reliable tip, sets off towards an address where he believes he will uncover vital information about the hit-and-run suspect.
Meanwhile, Han-na is entrusted with returning the victim's personal belongings. Upon learning of the victim's untimely demise, she decides to deliver them the next day and takes the possessions home. Suddenly, a gang of thugs deceives her into letting them into her home, their true intention being to search for important documents. As they launch their attack, Han-na draws her gun with swift precision and fires at them, defending her territory with unwavering courage.
Elsewhere, Dong-ju storms into a gangster lair, brimming with combat readiness. Simultaneously, Jong-hyeon finds himself besieged by a pack of thugs in the middle of a bustling road, hired by a vengeful policeman who harbors deep resentment towards him. Jae-hong chances upon this brutal assault and cannot look away.
Each combatant unleashes their unique fighting prowess: Dong-ju, a seasoned boxer, displays his rapid-fire punches; Han-na, adept with a firearm, sharpens her aim; Jong-hyeon, a master fencer, parries with elegance and precision; Man-sik, a wrestling giant, employs his immense strength and agility; and Jae-hong, a formidable discus thrower, demonstrates his amazing strength by hurling an enormous iron manhole cover at a speeding vehicle that barrels towards him. The scene culminates on this exhilarating cliffhanger, leaving viewers on the edge of their seats!
