Episode 1 of "Twelve" kicks off with a narrator weaving the ancient tale of the Twelve angels. Following the creation of the world by Light, twelve celestial beings were dispatched to safeguard humanity. Each angel possessed unique animal-inspired abilities, serving as their shield in protecting the humans. As the realm created by Light blossomed, the domain of Darkness shrank. Enraged, Darkness unleashed malevolent spirits upon the world, intent on sowing discord. United, the Twelve angels made a solemn sacrifice to preserve the human world. In a fierce confrontation, they emerged victorious, imprisoning the evil spirits within the ominous Hellmouth. Depleted from the epic struggle, the surviving angels relinquished their divine powers and continued their existence on Earth, incognito as humans.
Enter Tae-san, the preeminent leader of the Twelve and the CEO of Angel Capital Group, a financing entity that extends loans solely to gangsters and ex-convicts. Tae-san is currently preoccupied with collecting a debt from Jo Yang-su, who finds himself behind bars. Yang-su, defiant, mocks Tae-san's demands for his cars and properties, vowing to settle the account upon his release. Tae-san, unperturbed by Yang-su's bravado, warns him of the consequences before exiting.
Later, Tae-san dials Gwi-dol, instructing him to arrange Yang-su's bail. Meanwhile, back at the office, Mal-sook, Won-seung, and Kang-ji delve into a separate case, having received a tip-off from Gwi-dol.
Elsewhere, Detective Ma-rok reaches out to Tae-san, seeking a loan. With the funds, Ma-rok indulges in a shopping spree for Mir, unaware that she and Tae-san once shared an intimate past. A decade ago, Mir deserted Tae-san, embarking on a new journey at the local museum where she educates children about the history of the Twelve. When Mir encounters Ma-rok with the gifts, her expression sours; she declines the clothes, cognizant of their origin from Tae-san.
Ma-rok is plagued by anxieties, convinced that Mir's recent distance stems from a haunting prophetic dream she experienced. Tragically, Mir remains tight-lipped about the dream's contents, shouldering the burden in solitary confinement. Elsewhere, Bang-wool and Do-ni find themselves toiling at an oriental clinic, where Do-ni fears Bang-wool's intimidating bedside manner might be chasing away potential clients. Despite his diligent efforts to publicize the clinic, patients are often frightened by Bang-wool's demeanor during treatments.
Later in the evening, Yang-su gathers his cronies and girlfriend to celebrate his freedom. However, his euphoria is shattered by a call from Tae-san, announcing his imminent arrival. Yang-su, tense with apprehension, instructs his men to eliminate Tae-san on sight. To Yang-su's dismay, Tae-san proves to be an insurmountable force, swiftly dispatching all of Yang-su's lackeys. Witnessing this display of prowess, Yang-su cowers in submission, hastily apologizing and settling his debts.
Across town, Mal-sook, Won-seung, and Kang-ji embark on a collection run at a gambling den. As the den's boss attempts to flee, Do-ni steps in to lend a hand. Within moments, the trio reduces the gang to a pulp and secures their payment.
After collecting from Yang-su, Tae-san pays a visit to his old friend, Geum-soon. He regards her as the sole human with whom he can openly converse, having known her since childhood when he rescued her family from ruthless debt collectors. Now, Geum-soon, like her mother before her, operates a Tteobokki stand. Despite her advancing years, Tae-san still views her as a child.
As they reminisce, Geum-soon acknowledges Tae-san and the angel's arduous work and selflessness. She empathizes with the pain caused by his lost family and the ingratitude of humanity. She endeavors to uplift him, reassuring him that most humans are good-hearted and appreciative of their sacrifices. Tae-san attempts to give her money, but she politely declines.
Their conversation is abruptly interrupted by an elderly man who sternly reproaches Tae-san for addressing Geum-soon informally. Tae-san recognizes the man as Man-book and is astonished to see that he has aged not a day. They embrace warmly, their friendship undiminished by time.
At the police station, Ma-rok savors his meal while glancing at the news. The broadcast reveals that numerous Palaeolithic relics have been unearthed at a construction site, destined for academic research at the NRIC. However, during the examination, scientists find it peculiar that the relics register no readings on the spectrum. Mysteriously, the relics exhibit abnormal spikes.
The scene seamlessly transitions to a cluster of individuals engaging in an obscure ritual amidst an isolated, barren landscape. A man deliberately slices his palm and presses it against a rugged boulder. Miraculously, his blood vanishes instantly, prompting them to assure their leader that they have pinpointed O-gwi's location with success.
Returning our focus to Tae-san, we witness his return to the empty company premises. He heads straight to his office, unlocks the safe, and proceeds to distribute the stacks of money within. For a fleeting moment, his face beams with contentment, but his demeanor swiftly shifts, engulfed by a wave of sorrow.
Meanwhile, amidst the malevolent spirits, the leader attempts another ritual but falls short. His companions caution him to refrain from pushing himself to the brink, fearing for his life. Undeterred, the leader insists that time is of the essence and makes another attempt. This time, he drove a knife into his hand, pinning it to the rock. His blood serves as an awakening talisman, rousing the demon confined within the stone prison.
A luminescent green light pierces the darkness, causing the rocks to tremble violently. In an instant, a figure with piercing red eyes emerges, commanding attention. The episode culminates with the man unfurling his wings to their fullest extent, their grandeur capturing the essence of the eerie, surreal moment.
