The premiere of "Trigger" kicks off with a gripping news broadcast highlighting the surge of anger among South Korea's youth. This emotional turmoil has led to a disturbing uptick in suicide rates and instances of intermittent explosive disorders, encompassing phenomena such as voluntary seclusion, road rage, violent outbursts, social anxiety, dopamine addiction, and domestic abuse.
Scene shifts to Officer Lee Do swiftly arriving at a chaotic road accident, where a nurse, dozing off behind the wheel, has collided with a car waiting at a red light. The other driver, fury etched across his face, is on the brink of explosion, but Lee Do deftly defuses the situation with his soothing demeanor.
Elsewhere, Jeong-tae boards the subway en route to school. A vendor, peddling gun-shaped lighters, startles some foreign passengers. As Jeong-tae journeys on, he encounters a pregnant woman standing while a man lounges in the designated seat for expectant mothers. Rule-abiding Jeong-tae, driven by a sense of justice, demands the man stand up. However, the woman intervenes, assurances that she'll alight shortly diffusing the tense situation.
Jeong-tae finally arrives at school, only to be greeted by a lecture's reprimand for tardiness. His mind wanders to a grim fantasy—pulling a gun from his guitar case and unleashing chaos upon his classmates. Later, in his psychology session, Jeong-tae confides in his therapist about the struggle to curb his lethal impulses. The psychologist gently reminds him that everyone harbors a trigger within, urging him not to let emotion override reason.
Meanwhile, a protest gathers momentum, drawing a crowd. Reporter Wang and his companion are hired to capture images that inflate the demonstration's scale tenfold. While Wang's friend suspects an ulterior motive, Wang remains pragmatic—protesters or not, they're paying the bills.
Across town, a landlord discovers a tenant's tragic suicide. Detective Seo and the forensic team uncover bullets in the victim's pocket, prompting a call to Officer Lee Do, an authority on military-grade ammunition and firearms. Lee Do's meticulous search uncovers additional bullets concealed in the ceiling, further deepening the mystery surrounding the death.
Later in the evening, Hyun-sik accompanies Officer Lee to a cozy drinking establishment after their workday concludes. With a stern tone, Hyun-sik cautions Officer Lee, despite his expertise, to steer clear of a particular case. He reproaches Officer Lee for neglecting to seek a promotion, given his extensive experience and remarkable abilities. Transitioning to a more personal grievance, Hyun-sik vents about his daughter's desire to strike out on her own and leave the nest. Eventually, Se-seong arrives to pick up Hyun-sik, wrapping up their conversation.
Back at his residence, Officer Lee's mind drifts back to his military days, a flood of nostalgia washing over him. The following morning, the precinct welcomes a fresh face in the form of a new officer, whom Officer Lee promptly takes under his wing as the designated training officer. As they venture out to address a citizen's complaint, Officer Jang exudes overconfidence, vowing to apprehend every wrongdoer and see them incarcerated.
Their destination: Oh Kyung-suk, a grief-stricken mother protesting outside a corporation for the negligence that led to her son's demise. Driven by financial desperation, her son had taken a perilous job with the company only to perish in an avoidable accident. The corporation, callous and unremorseful, refused to acknowledge any culpability or offer condolences.
Elsewhere, Jeong-tae finds himself at odds with the manager of his boarding house over stolen food items. Rather than addressing the issue, the manager dismisses Jeong-tae's concerns with contempt and physically ejects him from his office. Dejected, Jeong-tae retreats to his room, only to confront his loud, smoking, video game-playing neighbor who defies the boarding house rules with impunity. When Jeong-tae persists, the neighbor responds with aggression, assaulting him.
Sequestered in his room, Jeong-tae battles to maintain his sanity as the rage within him threatens to consume him. Reaching for his guitar case, he retrieves a concealed firearm and, driven by a tempest of emotions, creeps toward his neighbor's door, the trigger nearly engaging. At the eleventh hour, he wrestles back control, averting disaster.
In a separate incident, a saleswoman visits a residence to service a water purifier, unaware that she stands on the doorstep of a sex offender under house arrest. Narrowly escaping molestation, her fortune shifts when Officer Lee and Jang arrive, prompted by a malfunctioning ankle monitor. The shaken saleswoman flees, with Officer Lee giving chase to reassure her. He wisely advises her to consult the sex offender registry before entering any home in the future. While Officer Lee patrols the vicinity, Officer Jang inspects the ankle monitor, narrowly escaping a chopstick-wielding attack from the criminal. Officer Lee intervenes just in time, saving his colleague.
As Officer Lee and his fellow officers gear up for their nocturnal duties, Jeong-tae finds himself struggling to concentrate on his studies within the confines of his room. Unfortunately, his attempts at focus are repeatedly shattered by the raucous groans emanating from one of his neighbors' rooms, where an intimate encounter is unfolding with little regard for the walls that separate them. Despite his efforts to maintain composure and rein in his frustration, Jeong-tae eventually reaches his breaking point.
In a sudden surge of rage, Jeong-tae retrieves a firearm concealed within his guitar case and, without hesitation, discharges it. The ensuing shot startles the girl, prompting her to dial 911. However, Jeong-tae, now in a frenzy, snatches her phone and coldly informs the dispatcher of his deed, making it clear that their assistance is no longer needed. This grim pronouncement marks the beginning of Jeong-tae's lethal rampage.
He methodically targets his neighbors: first, the couple whose passionate noises had disturbed him, then the gamer whose relentless video game blaring had long been a thorn in his side, and ultimately, the boarding house manager, whose oversight he likely resented in some capacity.
As Episode 1 of "Trigger" concludes, Officers Lee and Jang are dispatched to the scene of the boarding house shooting. Meanwhile, Jeong-tae, having secured the premises by locking the doors, methodically reloads his gun. Amidst the chaos, a twisted thought crosses his mind—he demands to know who dared to partake of his meals, adding a chilling layer of personal grievance to his already dreadful spree.
