A person wrapped in a head scarf leads a horse down a dirt road with a wagon carrying what looks like a wooden coffin. The head scarf unravels in the wind, and we see that this supposed historical warrior with a sword is our protagonist, who we'll later know as Jang Man-wol (IU). A group of soldiers discover the blood-stained scarf and race on horseback toward their wanted suspect.
That night, Man-wol stops at a tent for food and a drink, and the serving woman wonders aloud who this mysterious warrior is. Irascible Man-wol complains about the tasteless alcohol and chatty woman, and she proceeds to pour the alcohol on the coffin.
The woman asks if someone died or if Man-wol killed someone. She knows that the only people that wander through this area in these harsh conditions have either killed someone or are going to kill someone. Irritated by this woman, Man-wol threatens to cut off her tongue, but the woman isn't frightened; rather, astutely asks what Man-wol is searching for.
Man-wol answers that she's looking for a lodge where the dead can rest, and the woman identifies this place as the Moon Lodge. Man-wol's eyes widen at the mention of this lodge, and she asks where she can find it. The woman says that only the dead can venture there and looks to the crowd of ghosts behind Man-wol.
The woman asks how many spirits lie in the coffin, and Man-wol sadly admits that these people died because of her. She then asks how many people Man-wol killed for the dead in the coffin, and short-tempered Man-wol draws her sword, demanding the woman to direct her to the lodge.
Noticing the engraving on the sword, the woman learns Man-wol's name, which means full moon. Man-wol tears up as she tells the woman that she's trying to take responsibility for the lost lives. Then, she holds the sword against her neck and prepares to kill herself if that's the only way for her to find this lodge.
The woman, a deity named Mago disguised in human form, pities Man-wol for thinking that taking her own life will make up for the death she's caused. But Man-wol claims that her life is the only thing she can sacrifice now and digs the sword into her neck. Mago reiterates that the dead gather at the Moon Lodge and looks to the horseback soldiers arriving behind Man-wol.
Man-wol positions herself to fight these soldiers, but they turn into dust as they ride past her. The woman tells that she's killed these soldiers before, and Man-wol remembers slaughtering them and picking up the bloodied scarf.
Holding the scarf in her hand, Man-wol looks at her deserted surroundings and wonders if she's arrived in the Moon Lodge as a demonic spirit. Mago has also disappeared, but her voice tells Man-wol, "You arrogant, foolish, and self-pitying human — now that you've walked into the place of your punishment, take responsibility for your sins."
Then, a shadow approaches from behind, and Man-wol turns to defend herself against the attacker, but she stabs her sword into a tree. Her past life suddenly flashes before her eyes, and she cries at the faraway memories. The tree pulls the sword from Man-wol's hands and absorbs it before growing taller with extending branches.
A sudden gust blows through and collects all the wood scraps to build a large lodge right in front of Man-wol and the mysterious tree. From afar, Mago comments that the Moon Lodge has met its new owner. She opens up the wooden coffin — full of bloody swords and ornaments — and tells the spirits that she will escort them to their resting spot. Then, she leads the horse on the night road lit by fireflies.
In the year 1998, a father (cameo by Oh Ji-ho) apologizes to his son for not getting him anything for his birthday, and the son assures him that it's okay. A couple passing by drops money, and when Dad tries to claim it in finders keepers style, the son shakes his head and returns the money to the couple.
The modernized Mago appears (this time as a women peddling flowers) and commends the boy's righteous actions, and Dad tries to wave her off. The woman tells the boy that his father is his misfortune, but she assures him that the suffering in early years will balance out to great fortune in the future.
Dad tries to dismiss the crazy flower seller and promises his son a birthday present. But the precocious young lad assures Dad that he doesn't need anything special for his birthday and requests that Dad not do anything dangerous to make money.
Then, they're interrupted by police sirens and an emergency search in the waterfront. The first responders carry a dead body out of the water, and the spirit also emerges and sees her own dead body. She also spots her potential perpetrator in the group of nosy spectators. Then, she looks to the full moon and disintegrates to dust.
In a sleek dress, Man-wol walks into her office, where we see photos of her and the lodge throughout the years, dating back to the early 1900s. She sees the full moon from her window, and her assistant, Manager Noh, notes that the full moon will attract many guests tonight. Man-wol seems annoyed by the impending flood of these bothersome spirits and tells Manager Noh to open for business.
Prickly Man-wol shares that the full moon always puts her in a bad mood, but she's especially cranky today. She orders Manager Noh to reject any spirits who've had extremely unnatural deaths. but Manager Noh calmly responds that they shouldn't discriminate against customers but promises to keep these unfortunate spirits out of Man-wol's sight.
Man-wol glares at the full moon and curses at this repulsive sight. The lodge opens for business, with the Hotel del Luna sign flickering on and the building unfolding into a large castle under the bright full moon.
In the night streets, Dad flees from the police with a chunky bag in his hands. He trips and rolls down a flight of stairs, and his body seems to go limp. But he gets right up, rubbing his head, and he runs off with the cash from the register.
While running through the streets, Dad notices Hotel del Luna and hesitates to walk into the building in case he needs to pay. As he dusts off his jacket and ties his shoes to look appropriate for this fancy place, the drowned ghost enters the hotel. The receptionist asks how long it's been since she's died, and she estimates around ten days. Dad watches them from outside and then follows them up the elevator to a large fancy lobby.
In the lobby, Dad sits across from the drowned water ghost and asks if they need to pay to just sit there. Water Ghost doesn't know since it's also her first time at the hotel, and Dad asks how she got so wet. Ghost says that she was in the Han River, and Dad finds that curious
Water Ghost notices the blood behind Dad's ear and asks how he injured himself. Dad explains that he rolled down the stairs and flinches when he touches the injury. At the end of the stairs, we see Dad's limp body with blood pooling around his head and his finger flinching ever so slightly. Wait, is he dead or alive?
Receptionist JI HYUN-JOONG (Block B's Pyo Ji-hoon) notifies Manager Noh that they've received their first water ghost in a while. Manager Noh tells Hyun-joong to escort the water ghost to a room as soon as possible to keep the unpleasant sight away from owner Man-wol. Then, Dad walks by and briefly makes awkward eye contact before scooting away
Manager Noh recognizes that Dad doesn't belong at the hotel because he's not dead yet and orders Receptionist Hyun-joong to quickly usher this unintended guest out of the hotel before Man-wol kills him. As Dad walks by a fancy vase with a gold snake, he's tempted to steal it but decides that he has other priorities for now. As he runs off, the gold snake comes to life and follows him.
Dad finds a sign to an outdoor pool and wanders through the door to a beach. He's greeted by the guest manager, CHOI SEO-HEE (Bae Hae-sun), who asks for his room number to further assist him. Dad politely declines the offer and runs back to the hotel.
Dad then wanders into the bar, where he's met by bartender KIM SUN-BI (Shin Jung-geun). He smiles sheepishly and heads up to the balcony, where he marvels at the height of the hotel.
Manager Noh notifies his team that they have a living guest exploring the hotel, completely oblivious to the hotel's purpose. Guest Manager Seo-hee worries that the living man will die if Man-wol learns about this, but bartender Sun-bi is more worried about their boss hanging this over their heads for at least 50 years.
Man-wol would repeat a catch phrase whenever they did something wrong — a threat to board them on the bus to the afterworld — and the team shudders at the thought of their impending scolding. Receptionist Hyun-joong worries that he's at fault for letting this man in, and the other two are ready to throw him under the bus because they have business to tend to in the living world. Ha.
Manager Noh worries that this man will never leave this hotel if Man-wol discovers him, but it seems to be too late. Man-wol notices that the gold snake on her vase has disappeared and figures that there must be a thief in the building.
Dad continues to obliviously tour the hotel premises and finds his way to the ancient tree. He sees flowers blooming on a branch and remembers his son, Chan-sung, asking for flowers for his birthday. He jumps to pick off the flowers, but a gust of wind knocks him to the ground. When he tries to get up, he's held to the ground by someone's foot. It's Man-wol.
Man-wol notices that Dad experiencing pain from her foot holding him down and deduces that he must still be alive. She accuses him of theft, and when he denies this, the golden snake slithers out of his jacket. She knows that he was planning on stealing and warns him that the snake bite could kill him.
Dad begs for mercy and says that he can't die. Man-wol coldly says that everyone eventually dies and explains that he's already dying, Dad notices his fading hands, and we see Dad flatlining at the hospital, with crying Chan-sung helplessly watching.
At the hotel, Dad pleads for his life, as he need to return to his son. Man-wol notices the blue flowers on the ground, and Dad explains that he picked it off the tree for his son's birthday. She doesn't believe him because the tree doesn't blossom, but he promises that it's true. She wonders if this is a sign to let this man live. Dad promises to live righteously and raise his son well.
Man-wol agrees to let him live, on one condition: Dad offers his son to Man-wol. She'll give him 20 more years to raise his son, but after that, she'll claim him. Starting to fade away, Dad desperately agrees to her terms to return to his son. She taps the top of Dad's head, and he jolts awake in the hospital room.
When Dad opens his eyes, Chan-sung calls for the doctors to check his Dad, who's just come back from the dead. Dad looks tearfully at his son, who continues to sob in shock. At the hotel, Man-wol realizes that she never gave Dad the flower to give to his son, and she throws it back at the tree. Upon reaching the tree, the flower fizzles into dust.
All bandaged up, Dad walks with Chan-sung at the hospital and recognizes the photo of the woman, whose funeral procession is escorted by her fellow police colleagues. The woman is the drowned Han River ghost, and Dad wonders if everything was a dream.
At the hotel, the Water Ghost tells Man-wol that she was a policewoman who was killed after being discovered during an undercover investigation. Man-wol unsympathetically relays her sympathies and informs Water Ghost that she'll be rewarded with a special ride to the afterworld, but Water Ghost has unfinished business in the living world.
Man-wol warns Water Ghost that revenge is futile and advises Water Ghost to move on from her past life to reap the rewards of her honorable death in her next life. But Water Ghost insists that she must stay to catch the criminal she was pursuing because the murderer supposedly can't be reached by law.
With a hint of annoyance, Man-wol notes that Water Ghost carries a lot of responsibility and asks if Water Ghost has any money saved up to pay for services in the living world. Water Ghost nods, and then Man-wol immediately puts on her best customer service smile to offer her help. Water Ghost reaches into the back of her head and pulls out a slimey bullet. Man-wol takes it and smiles.
At an award ceremony, Mayor Park Gyu-ho (cameo by Kim Won-hae) awards a local businessman — who we saw suspiciously walk away from the scene of the Han River body discovery — with an innovative business award. They're interrupted by a piercing audio feedback sound, and all the cameras turn off. The door opens, and Man-wol walks in with her fancy shotgun.
Mayor Park yells at everyone to stop this woman with the gun, and the revived cameras turn to where he's pointing to find nothing. Man-wol is only visible to him. She cocks the gun and shoots Water Ghost's bullet directly at Mayor Park's chest. The mayor caves in pain and announces that he's just been shot, but he finds no wound. Then, from behind, he sees Water Ghost, or Officer Lee.
The cameras catch Mayor Park freaking out and desperately crawling away from this ghost, while confirming with the businessman that he killed Officer Lee. He says this in front of rolling cameras, and Officer Lee cries at this confession. Mission complete, Man-wol walks out with a satisfied smile.
Manager Noh commends Man-wol for this proxy punishment, and Man-wol presumes that Officer Lee will return to the hotel after sufficiently torturing her perpetrators. She asks Manager Noh if he retrieved the ghost's payment, and he reveals a pile of diamonds that Officer Lee confiscated from criminals.
Man-wol looks delighted that these diamonds will cover her champagne costs, but Manager Noh takes half of the diamonds to pay off loans and then an additional half of the remaining diamonds to pay off future loans. Man-wol scolds Manager Noh for poor management of hotel funds, but Manager Noh clarifies that these loans are for Man-wol's personal expenses — her car, shopping, and champagne.
Man-wol complains that she never needed to worry about money with her former manager. Manager Noh reminds her that the manager before that had her suffering through a farming austerity and suggests that she invest the remaining diamonds in the 20-year nurture of her new manager.
Man-wol reluctantly agrees to Manager Noh's suggestion and vows to work Chan-sung hard when he grows up. When Dad receives the large sum of money in his bank account, he determines that what he experienced yesterday wasn't a dream. Bandaged and hobbling on his crutches, Dad sets out to find this hotel and return the money.
As Chan-sung waits for Dad, a car pulls up. The windows roll down to reveal Man-wol, who inspects the child and smiles. Man-wol tells Manager Noh to send flowers — evening primrose flowers — every year for Chan-sung's birthday so that Dad never forgets his promise.
We jump to the present in 2019, and we see grown GU CHAN-SUNG (Yeo Jin-gu) interviewing for a hotel manager position in Korea after working in Singapore. He explains to his interviewer that he had declined the offer last year because he had promised his late father that he would stay out of Korea for 20 years. Having overcome that barrier, he's decided to take the offer. He figures that it was his father's ominous superstitious beliefs that prompted this promise.
Just in case, Chan-sung asks about a hotel covered in ivy, with a sky bar on the 100th floor, and a beach-like outdoor space that may have existed 20 years ago. The interviewer looks confused, and Chan-sung looks relieved that this hotel is surely imaginary.
As Chan-sung gets escorted to his office, he's informed that a birthday present arrived for him. Chan-sung stops in his tracks and mildly panics when he hears that the birthday delivery was flowers. In his office, he wonders what the flower delivery means, since it's been over 20 years now. He finds a letter attached to the delivery from Hotel del Luna.
Chan-sung opens the letter and finds a hire letter from Man-wol requesting that he start his new job the next day. There's even a map of the location in Myeongdong. At the subway station, Chan-sung wonders if he should visit the hotel, but he decides against it and throws away the flowers.
In the subway, Chan-sung squeezes through the crowds and enters the next train, which he finds completely empty except for Man-wol, sitting with the flowers he just threw away. Chan-sung confronts Man-wol and asks if she's come to collect him now. He's well aware that he's been sold to her and that she had sent him flowers every year for the past 20 years.
Chan-sung admits that he felt uneasy every year when these flowers arrived and acknowledges that he jumped from country to country to avoid her. He didn't expect her to actually come to collect him, as he believed the deal was over at the 20-year mark last year.
Man-wol slyly says that she let him off the hook for a year, so she expects him to come work for her starting tomorrow, as promised. Based on his father's warnings, Chan-sung knows that Man-wol is a scary person, so he asks if she will kill him if he declines her offer.
Man-wol realizes that Chan-sung doesn't fear her yet and figures that her beauty masks her menace. Chan-sung acknowledges this and reject her job offer. She regrets sending him flowers every year and says that she should have sent him a beheaded canary instead.
Determined to instill fear, Man-wol offers a different birthday present this year. The train lights turn off, and Man-wol slowly approaches Chan-sung, who pleads that she give up on him. She strokes his face, and Chan-sung asks if she plans on beheading him like the canary she spoke of. Then, she blows on his face.
Chan-sung closes his eyes, but nothing happens. Man-wol wishes him a happy birthday and assures him that this gift will be very special. The train returns to normal, and he leaves, Chan-sung reclaims the flowers and explains that he only threw away the flowers because they would need to be inspected when he crosses borders. Man-wol looks amused by Chan-sung's unassuming nature.
As Chan-sung walks home, he wonders what Man-wol did to him. He imagines Man-wol seductively stroking his face and wonders if he's become a toy. Then, he remembers his old father firmly ordering Chan-sung to run away if he ever met Man-wol, so he runs home to pack his things.
Chan-sung's vision gets blurry as he packs his suitcase and when he goes outside to hail a taxi. Then, he notices that a pale woman in sunglasses appears in front of him.
At the hotel, Man-wol seems satisfied with her gift of vision — that is, vision of the dead. Manager Noh shares his concerns that giving Chan-sung this vision without any forewarning may cause more trouble and possible harm. Man-wol belatedly realizes this and figures that a dead Chan-sung wouldn't be useful.
Chan-sung spots an upcoming taxi and tells the pale woman next to him that he has first dibs. The woman turns to him, and he tries to confirm that she must have seen him waiting. The pale woman says that she can't see, and then takes off her sunglasses to reveal two bloody holes where her eyes would have been. Ah!
Shocked at this sight, Chan-sung rubs his eyes and realizes that he's witnessing a dead person. He gapes as this dead person walks past him, staying silent so that the ghost can't follow his voice. But when the taxi arrives, the ghost immediately turns around to the sound of Chan-sung's voice talking to the taxi driver. Petrified by the ghost, Chan-sun fails to get into the taxi and runs for his life.
Man-wol follows Chan-sung as he flees with his suitcase in tow. He runs into the ghost at an unexpected corner and then yells as he runs in the opposite direction. After multiple laps around the neighborhood, Chan-sung opts to hide, but mischievous Man-wol peers over the ledge to drop a stone on him. That's enough to startle scaredy-cat Chan-sung, who runs off screaming once again.
Chan-sung finally gets cornered by this ghost, and Man-wol watches with amusement. He yells at her to go away, and when she tries to take off her sunglasses, he yells at her to stop. "I know that you have no eyes, but it's so scary!!!" LOL, I love this.
Showing some mercy, Man-wol intervenes and covers Chan-sung's mouth. Once he falls silent, Man-wol throws a pebble in the opposite direction, and the ghost follows the sound and leaves. Chan-sung gets himself together, and Man-wol says that her gift will accompany him across borders and can't be thrown away like the flowers.
Chan-sung asks if Man-wol sent the ghost to him, and Man-wol clarifies that he can just see what he couldn't before. He's crushed by this new frightening reality. Man-wol suggests that they go find a good restaurant she saw on TV, and Chan-sung seems incredulous by her casual suggestion to grab a bite together.
Chan-sung asserts that he won't go to the restaurant with Man-wol until she returns his eyes to normal, but Man-wol has the upper hand here. She warns him that if they don't make it to the restaurant in time, then he'll have ghost vision forever.
At the restaurant, Chan-sung keeps his eyes closed in fear of seeing more ghosts while Man-wol takes pictures of this famous foodie location. Outside, a homeless man eats leftovers and recognizes Man-wol as the woman who shot the gun at him. Aha, he's Mayor Park. He remembers her and looks ready for revenge.
Inside the restaurant, Man-wol tries to assuage Chan-sung's concerns about seeing terrifying ghosts all the time by pointing out a harmless child ghost in the restaurant. She says that most ghosts are like this — either because they haven't realized that they're dead or because they find something they were obsessed with in life.
Chan-sung finds Man-wol extremely strange and asks if she's dead or alive. Looking a bit somber, Man-wol says that she's not dead yet — she's merely existing for now. He wonders if that implies that she'll die one day, and she jokingly asks if he'll kill her. Chan-sung only wishes for Man-wol to disappear from his life.
As they walk through the streets, Man-wol orders Chan-sung to buy some milk tea and threatens to kill him if the shop closes on them. After he leaves, Man-wol spots the indignant former mayor from the corner of her eye and prepares to confront him. The mayor recognizes her as the shooter, and Man-wol informs him that his afterlife will be even worse than his current life.
The foul mayor blames Man-wol for his ruined life and stabs her with a sharpened rod. He laughs at his successful stab, and Man-wol remembers her former sword fights. As the mayor walks away, Chan-sung worriedly runs to Man-wol to check if she's okay.
Disheartened by how her actions mirrored the mayor's attack, Man-wol wonders why humans never acknowledge their own wrongdoings and always blame others. Man-wol gives Chan-sung one opportunity to walk away from her now and have her disappear from his life. After a moment of hesitation, Chan-sung runs away from her.
Man-wol sits against the light post like a ragdoll and closes her eyes in defeat. Then, Chan-sung reappears with a wagon in tow to carry Man-wol. He worriedly tells her to get into the wagon and wipes away the dirt in the back, but Man-wol gets up on her own just fine. She pulls the rod out of her chest and calls Chan-sung weak.
When Chan-sung tries to leave, she doesn't allow him. She suspends the rod in the air, and for a moment, Chan-sung suspects that she's going to kill him. But the rod shoots past him, through the alleyway, and pierces the former mayor, who crumbles into dust. Man-wol says that Chan-sung missed his opportunity to leave. "Now, if you run away, I'll kill you."