Geumbok arrives in Seoul with dreams of becoming an actor, only to fall victim to a housing scam that leaves him homeless. To survive, he takes a job at a cafe, donning a mascot costume to attract customers, but ends up mocked and bullied. Just as despair sets in, a mysterious man named Bihyung appears, his overwhelming aura driving others away. To Geumbok’s shock, Bihyung embraces him, whispers, “You are my master,” marking the beginning of a fateful entanglement.

Bihyung, the half-human, half-divine king of goblins, carries a fatal weakness; unlike others of his kind, he cannot absorb human essence to survive. Without ever meeting his destined master, he has endured centuries of frailty and loneliness. In the present day, Bihyung brings Geumbok to his home, where their roommate Gildal discovers something extraordinary: for the first time in a thousand years, Bihyung shows no rejection toward a human, and even his wounds begin to heal. Tempting Geumbok with free rent, Gildal invites him to stay, determined to uncover the secret bond between them.

Long ago, there was a guardian stone passed down for generations, believed to be a fragment of the mountain god that could distinguish good from evil in human hearts. Bihyung discovered this stone and invited it to join him in protecting the world. The stone took human form and was named Gildal. In the present day, Geumbok helps Gildal with household chores, and Gildal reveals that he resembles someone from Bihyung’s past who mysteriously vanished. Meanwhile, Bihyung senses a strange aura around Geumbok. Samshin warns him that this energy could attract spirits and monsters, placing Geumbok in great danger.

A child born between a human and a nine-tailed fox was rejected by both worlds and wandered alone until he met a queen who awakened his passion, giving him the name Jigwi. In the present, Geumbok’s spiritual gate has opened, drawing evil spirits toward him. To protect him, Bihyung makes a contract to temporarily share his power. Hoping to appear more confident, Geumbok visits a plastic surgery clinic, where the handsome doctor turns out to be Jigwi himself who boldly asks him out on a date.

Jigwi invites Geumbok on a date, intending to confess his feelings, but Gilda steps in to stop him and warns Geumbok not to be deceived. It is revealed that Gildal and Jigwi were once close friends until Jigwi betrayed their master, Bihyung. Despite the betrayal, Jigwi still holds feelings of guilt and nostalgia toward Gildal. Meanwhile, Geumbok unexpectedly receives a call from an acting agency offering him an audition. Overjoyed, he asks Bihyung and Gildal to help him rehearse a romantic scene together.

Geumbok goes to an entertainment agency for an audition and is asked to pay three million won in training fees. This time, Geumbok is smart enough not to fall for the scam. Later, Jigwi invites him out, where their flirty conversation is suddenly interrupted by Gilda’s unexpected appearance. That same night, Gildal encounters Jigwi at a bar. Old grudges resurface as they accuse each other of betraying Bihyung, and Gildal warns Jigwi never to approach Geumbok again.

Jigwi wakes up after a night of drinking to find Gildal lying on his bare chest, and he gives a conflicted smile. When he steps out of the room, he encounters Bihyung, and old grudges resurface. Gildal, confused by his feelings, begins to wonder if he truly likes Jigwi, while Geumbok suspects that Bihyung and Jigwi are hiding a secret. That night, Geumbok is attacked by an evil spirit, and Bihyung rushes to save him once again — as love and danger draw ever closer.

On the night of the year’s largest full moon — a rare total lunar eclipse said to be perfect for confessing one’s love — Geumbok decides to move out of the goblin’s house and focus on his dream of becoming an actor. At the same time, Gildal makes a bold decision and confesses his true feelings to Jigwi. Saddened by Geumbok’s decision to leave, Bihyung takes Samshin’s advice and resolves to win him back. But as he gathers his courage, the evil spirit begins to stir once again in the darkness.

Bihyung falls into a deep coma, and without the spiritual energy of his master, he may never awaken. Yet his master had vanished a thousand years ago. Samsin pleads with Geumbok to travel back in time to find that person. As Samsin performs the ritual, Geumbok lies beside Bihyung and slowly drifts into sleep. When he opens his eyes, he finds himself in an old, decaying house of the past—only to face Bihyung holding a dagger to his throat, mistaking him for a spy sent by the enemy.

It turns out Geumbok was Bihyung’s master from a thousand years ago! Back in the present, Bihyung finally awakens and begins treating Geumbok with utmost devotion—like a true “master” of the Goblin King. He gives him a black card with a 50-million limit, hires a home-cleaning service, and even cooks for him himself, barring Gildal from getting close. Meanwhile, the tension between Gildal and Jigwi grows increasingly intimate.

Bihyung and Geumbok’s relationship deepens rapidly, but the next morning, Geumbok vanishes—leaving behind the gourd pendant and a farewell letter. To return to the past and save Bihyung, he must erase all memories of the goblins and resume his life as a human, breaking Bihyung’s heart. Meanwhile, Gildal discovers Geumbok’s handkerchief and realizes the story isn’t over. Yet when he witnesses Jigwi entangled with his former lover, his heart shatters all over again.

Geumbok stars in a goblin-themed film and quickly rises to fame as a popular new actor. During an interview, he confesses that his first love was a goblin. One day, he returns to the old café filled with memories and Bihyung appears. Has the love between the master and his goblin finally begun for real?