Episode 5 of "Trigger" kicks off with a poignant flashback to the heartfelt bond between Lee Do and Kyung-sook. On a bitingly cold day, Lee Do chances upon Kyung-sook, her frail frame battling against the elements as she protests outside a company, demanding justice for her son. moved by her plight, Lee Do offers her a ride home, and in gratitude, she presents him with a jar of kimchi, her heartfelt token of appreciation. With warmth in her eyes, Kyung-sook confesses that she views Lee Do as her own flesh and blood.
After escorting Kyung-sook to the hospital, Lee Do bids farewell to Moon-baek and embarks on a quest to locate Seok-ho, to no avail, but crossing paths with his henchmen instead. Meanwhile, Detective Seo arrives at the hospital, where Jung-man's henchmen lie injured and confined. Lee Do reaches out to him, instructing him to procure an address list, which proves crucial in their investigation.
Later, Detective Seo and Lee Do converge at Kyung-sook's humble abode. Lee Do briefs Detective Seo on the guns and their distribution network, relaying this vital information to the police team at the station. Acting swiftly, Chief Yoon directives the team to scrutinize each address on the list, verify if firearms are present, and confiscate them accordingly.
Back at the hospital, Lee Do discovers Moon-baek still lingering. Curiosity piqued, Moon-baek inquiries about Lee Do's maternal bond with Kyung-sook. Lee Do explains that it stems from her motherly affection towards him. In a heart-wrenching revelation, Lee Do shares that his own mother is deceased, prompting Moon-baek to disclose his own tragic backstory – abandonment at an orphanage's doorstep.
Flashing back to a chilly day, Moon-baek's mother stands hesitantly before the orphanage. Just as she's about to leave him at the threshold, another woman steps forward, posing as a savior, promising to rescue him from the orphanage's clutches. Unbeknownst to them, she is part of a sinister gang involved in organ and human trafficking.
Horrifically, Moon-baek's ordeal begins with the brutal extraction of one of his eyes to fulfill a lucrative buyer's demand. Abandoned and shuffled between foster families, his life takes another desperate turn when he's sent to the United States, hoping for a fresh start. Instead, he finds himself entangled in the clutches of another trafficking ring, systematically having his organs harvested. Miraculously, the FBI intervenes, rescuing him from his nightmarish existence.
At school, Seung-jin and his cronies persist in bullying Gyu-jin, but this time, Gyu-jin stands his ground and retaliates. When they invite him to join them at karaoke later, he defiantly declines. In class, Seung-jin escalates his aggression, using a sharpener as a threat to coerce Gyu-jin into insulting their teacher. Gyu-jin's patience snaps, and he charges at Seung-jin, shouting for him to cease his actions.
Elsewhere, Seok-ho seethes with rage as Lee Doo storms into his territory and attacks his men, sparked by the involvement of U-tae. Yong-gu recognizes U-tae as a member of Jung-man's crew. Meanwhile, Jung-man makes his way to the hospital to visit U-tae and the injured boys, only to be blocked by the police at the door.
As he exits, Jung-man crosses paths with Lee Do and Moon-baek. Realizing that Lee Do is behind the ordeal of his men, Jung-man intends to confront him. However, Moon-baek notices Jung-man's intent and interposes himself between Lee Do and danger.
After dining and imbibing together, Moon-baek and Lee Do part ways. Officer Jang later picks up Lee Do, while Jung-man tails them discreetly. However, a sudden call from Seok-ho disrupts Jung-man's pursuit, urging him to meet immediately. Jung-man obliges and halts his pursuit of Lee Do.
Post-dinner, Moon-baek returns to the hospital's underground parking, where a luxurious car awaits him. One of his men had driven the BMW to the hospital with Kyung-sook, while Moon-baek arrived in a Rolls-Royce. Despite residing in the apartments Officer Jang had previously uncovered, Moon-baek's quarters are a penthouse, and he commands a group of men dressed in black at his bidding. It transpires that Moon-baek is the gang leader and the mastermind behind the influx of guns in the country.
A flashback unveils Moon-baek's origins. As a teenager in the US, Moon-baek ambushed the men who had harvested his organs. The gang was in the midst of brokering a deal for guns with a dealer named Jack. Jack, impressed by Moon-baek's indomitable fighting spirit despite his weakened state, takes him in, treats his wounds, and even provides him with a new eye. Consequently, Moon-baek sports a striking contrast of one blue eye and one black eye.
Earlier at the hospital, Lee Do recounted to Moon-baek a harrowing tale from his village. A mysterious individual had left a gun in the town square, which inexplicably vanished soon after. This strange occurrence was followed by a series of brutal murders, plunging the villagers into a paranoiac frenzy of fear. Desperation set in, and soon, every soul craved a weapon for their own protection. Yet, paradoxically, these arms became the instruments of their mutual destruction as they turned on one another in a bloody rampage. Regarding the enigmatic gun-placer, Lee Do revealed that his identity remained a mystery, though whispers suggested he was an Asian man with piercing blue eyes — an intriguing detail considering Moon-baek himself possessed one such eye.
Returning to the opulent penthouse, Moon-baek seethed with frustration as events unfolded far from his meticulously crafted plan. A significant portion of the firearms he had entrusted to Mr. Kim remained undistributed among the populace. He laid the blame squarely on the shoulders of the individual who had selected Mr. Kim, ultimately leading to the latter's untimely demise.
In a climactic moment at the conclusion of Trigger Episode 5, Moon-baek removed his contact lenses, revealing his natural blue eye, and fixed his gaze upon a digital screen mapping the distribution of their firearms. Red pins dotted the entire country, each one signifying the location of a gun, painting a grim picture of widespread armed readiness.
