In Iceland, a woman covered in ash comes out of a tunnel hidden under an active volcano called Katla. This volcano has been erupting for a year and huge clouds of ash cover the area. Nearby in the town of Vic, most locals have been evacuated and those who remain work on tasks related to the volcano like rescuing lost tourists cleaning the bodies of animals killed by the ash and studying the glacier.
Griema works as part of the rescue squad and her husband Kyrton takes care of their farm. Lately, their relationship has been on the rocks because he wants to leave, but she doesn't. Not to mention Griema's depression that makes her aloof. Her father, Thor, visits her often and insists the couple should move to the city to start a new life.
However, Griema refuses to leave because she hopes she can still find her sister Asa, who disappeared when the eruption began. Meanwhile, vulcanologist Dari looks at the latest samples from Kotla and notices significant changes. He decides he'll have to travel to Vic to investigate. At the observation post, AA and Leafer see the ashcovered woman wandering around.
They immediately get in their car and rush to rescue her. When they take her inside, she finally speaks to ask where she is. Soon, police chief Gizla is called to take care of the stranger. Before leaving, a doctor tells him that his wife Magnea won't survive for long if she continues to live there.
Because of cancer, her lungs are weak and the ash makes it hard to breathe. Gizla claims that he's tried to convince her to leave, but she refuses. Gizla picks Griema up and on their way to the observation post, they almost drive into a creasse in the glacier that wasn't there before. Thankfully, they stop the car just in time.
The duo takes another route and makes it to their destination where they learn that the mysterious woman is called Gunnhild and claims she knows Thor. They take Gunhill to the clinic where a nurse starts cleaning her up. Gunhild says she has to go to work claiming she's an employee at Hotel Vic.
Moments later, Thor arrives and stares at Gunnhild in shock before running away. Griema follows him home where he's burying a dead bird. She asks about Gunhild, but he refuses to answer any questions. Gizla goes to the hotel and asks manager Bergrun about Gunhild. Burgrun explains she's the only person working in the hotel now, but there was an employee named Gunnhild around 20 years ago.
Gizla then takes Bergrun to the clinic and Gunhild immediately recognizes her. She even apologizes for missing work days. Later at the hotel, Bergrun searches the old files and thanks to a photograph, she confirms that the woman in the clinic looks exactly like the Gunhild who worked there decades ago. Bergrun calls Gizla to pass this information with every personal detail she found.
Gizla calls the number on the file and Gunhild's son, Bujornne, picks up. He says his mother lives there, but she's not home at the moment. In the evening, Thor is having dinner when he hears a strange sound outside. He comes out and is shocked to discover that the bird he buried is standing there alive and well. Feeling very confused, Thor digs in the grave and finds the same body he buried earlier.
He compares it to the living bird and confirms they're the same because they have a matching white feather in their black bodies. In the meantime, Griema tries calling Gunhill's home again and tells Bjornne what's happening. He asks to talk to Gunnhild and he's shocked to hear her voice because it sounds just like his mother. But Gunnhill doesn't recognize him.
At that moment, an older Gunhild comes home and Bjornne gives her the phone. This old Gunnhild asks the woman in the clinic what her intentions are, but young Gunhild just feels lost. She explains that she's in Vic and that the only person she knows is Thor. Hearing that name causes old Gunnhill to hang up.
The next day, Gunnhill tells Bjornne that she'll go to Vic, ignoring his concerns about the volcano. Meanwhile, Griema is sending out weather balloons when suddenly she notices that the door of an abandoned building is open. She goes to investigate and finds blood on a cracked window. Then she goes inside and is shocked to find her sister Asa covered in ash.
A year ago, the rescue team had been riding their snowmobiles to reach the glacier because they had to rescue some tourists. Because of all the ash, the team didn't notice that Asa's ride stopped working and they continued to move ahead, leaving her behind. Asa tried using the radio, but it wasn't working.
When the team reached the observation post, Griema realized that her sister was missing and tried to call her, but her radio wasn't working either. Later, Asa's snowbike was found stuck in a crevice with no body, so Asa was presumed dead. In the present, Asa is surprised by the lack of people in the area and says she's always been there before passing out.
Griema calls an ambulance and Asa is taken to the clinic for treatment. Once she's been cleaned up, Gizla asks about her disappearance. Asa says that she remembers the rescue mission and feeling someone injecting her with a needle, but everything after that is darkness. When Thor arrives, he gets emotional as he hugs his daughter, who doesn't understand anything.
Meanwhile, Dari informs his wife, Rockl, that he's leaving on a trip. She wants to discuss their relationship, but he refuses, saying that's in the hands of the divorce lawyers now. Rockl calls Dari out for his attitude, pointing out that sooner or later he needs to move on from their son's death. A few hours later, AA and Leafer pick Dari up when he arrives at Vic.
They go to the observation post to look at the new samples, and Dari immediately notices more anomalies. That night, Griema falls asleep in the tub and has a dream of her mother walking into the ocean. She decides to visit the grave and her sadness is made worse by seeing the farm animals suffer under the ash.
At the clinic, the doctor informs Gunnhill that her tests came out fine and that memory loss is a normal symptom of hypothermia. The doctor also reveals that Gunhild is pregnant, which leaves her in shock. The next day, old Gunnhild tries to take the ferry to Vic, but she's told she needs a permit. Because of the volcano, it's become a closed area and only emergency workers or their relatives are allowed.
Gunhild explains that she was summoned by Gizla, but when the ferry driver calls the cop, he's told that nobody asked Gunhild to come. In the end, the man takes pity on her and agrees to take her to Vic. At the clinic, Asa tries to leave, but the doctors force her to stay for observation. After confirming she's doing well, they allow her to leave.
Griema is told that maybe Asa may have been kidnapped and held captive for the whole year. When the sisters leave, Griema hugs Asa and reminds her that she loves her, but Asa feels awkward. At the farm, Asa looks at her own obituary and asks questions about her funeral. She decides to visit the cemetery and sees her own grave next to her mother's.
The strange bird from earlier flies by and perches on Asa's arm, so she calls it her friend. Soon, old Gunhild arrives at the hotel and meets with Bergrun. They both recognize each other from the old days and reminisce. Gunhild explains she needs a car, and Burgrun tells her it's become acceptable to take any abandoned vehicle from the street.
Then Gunnhild goes to the clinic and meets the mysterious woman getting quite a shock when she notices that she looks like a copy of her younger self. Old Gunnhild asks about Thor and the young woman says that he got her pregnant. Afterward, Gunnhild visits Thor and tells him that the other Gunnhild said. Thor is confused since he never touched that young woman.
That night, the sisters are riding together and finally laugh while sharing memories. Suddenly, Griema has to stop the car because there are animals on the road. They look closely and notice blood on their fur. When they arrive home, Asa gets angry because Gunhild is having dinner with her family. Meanwhile, Dari hears someone moving in the shadows.
He goes searching for the intruder and finds him hiding in the bed. When he moves the blankets, he's shocked to find his son Mikuel covered in ash. A flashback shows Asa and Griema as children running around the house and jumping on the bed. Their mother suffered from mental health issues and found the situation overwhelming.
Suddenly, Griema heard a noise and went to the kitchen to find the food burning, but her mother was nowhere in sight. The mom left her robe behind, implying that was when she left the house to selfdelete. In the present, Griema discovers that one of the cows is dead and the mysterious bird is standing on it.
Kyan explains that the cow escaped last night and got contaminated, so he had to kill her because they can't produce polluted milk. At the observation post, Leafur and AA notice that Dar is acting weird. He says he just didn't sleep well and that he'll have breakfast in his room. Dari gives his food to Mikuel, who remembers eating his mother's cooking last night.
Mikuel tries to go to the bathroom, but Dari blocks the door and makes him pee in a bottle. When Leafer and A leave to get more samples, Dari doesn't join them with the excuse that he's getting the flu. After the duo is gone, Dari brings water to start cleaning Mikuel while asking him some questions about family life to confirm it's really him.
Mikuel answers everything perfectly and even remembers the time he cut his parrots wings off with scissors. After cleaning the boy up, Dari does a quick checkup to confirm his health is fine and notices a wound on Mikuel's knee. Dari also takes a blood sample while ignoring Mikuel's pleased to see his mother.
At home, Griema thinks Asa has been acting very differently and tries asking her questions, but Asa doesn't remember anything from the past year. Griema shares that she wanted to keep looking for her, but she had a very bad breakdown and her doctor advised her to drop the search. Asa says that maybe they would have found her sooner if they hadn't given up, causing Griema to storm off.
When Griema returns to the house, Asa is gone. She desperately searches the whole town until she finds her at the park. They argue about the way things have changed and Asa cries as she agrees not to leave the house without warning again. The sisters then enter an abandoned store and take a couple of swimsuits. On their way to the hot springs, they bond over the impact of their mother's death.
Eventually, they go swimming with their new swimsuits, only for Griema to freak out when she hallucinates that her mother is in the water with them. She quickly resurfaces and freaks out again because she can't see Asa, who suddenly startles her from behind as a prank. Griema is in a bad mood on their way home and says they should find an explanation behind Asa's return.
In the crevice, Leafer uses a chainsaw to get more samples, although all the layers of ash look the same. Nearby, Gizla has brought Magneia on a ride while he hunts for animals. Magneia feels better than usual because she felt loved when Gizla dressed her up and even applied her makeup. Later, on their way home, Magneia hates the way the animals bodies bleed all over the car.
After Magneia falls asleep, Gizla is tempted to touch her, but he stops himself just in time. Instead, he takes some naughty magazines to the bathroom. At the clinic, old Gunnhill visits the younger one, who is in the middle of an ultrasound. After the doctor agrees to give them some privacy, old Gunnhill demands an explanation.
The younger woman swears she's Gunhild and that the baby is Thor's. She thinks he just won't admit it because he doesn't want his wife to find out. Old Gunhild explains that Thor's wife is dead, leaving her in shock. That night, Thor goes to the clinic and finds both Gunhilds. The mood is very tense, and it only gets worse when the subject of the pregnancy comes out.
When it's time for visitors to leave, old Gunnhill talks to Thor outside to point out that he looks at the younger woman the same way he looked at her 20 years ago, but he should remember they aren't the same person. She thinks young Gunhild is a stalker trying to scam him. Meanwhile, Mikuel tries to sleep and tells his father that he loves him.
Feeling really uncomfortable, Dari secretly takes Mikuel to the shed and tells him to spend the night there before locking him up. The boy cries as he pounds on the door, begging his father for mercy. After Dari falls asleep outside the door, Mikuel searches for an alternate exit and finds the emergency phone, so he calls her mother.
Rockl is driving and has to stop the car in the middle of the road to deal with the shock. Mikuel also finds a utility knife on a shelf. In the middle of the night, the power goes out and Leafer enters the shed to check the power box, only to discover someone cut the cables. Dari wakes up and desperately searches for Mikuel, who thankfully managed to hide before Leafer could see him.
After a dream about her sister being trapped under the sea, Griema wakes up and rolls away from her husband. Kyon confronts her during breakfast, pointing he's been patient because Griema was dealing with great grief. But now that Asa is back, she's still not happy. Griema only says that he doesn't understand. Asa notices this and wonders if the decline in their relationship is her fault.
Rockl easily gets a fairy ride because she's the wife of a scientist living in Vic. In the observation post, Mikuel tells Dar that he doesn't trust him. At that moment, he gets a call from Rockl, who tells him about the boy's call. Dari tries to convince her that it isn't the real Mikuel, but Rockl says she's going to Vic anyway.
Later at the hotel, Dari arrives with Mikuel, who immediately runs to reunite with his mother. Rockl cries as she hugs her child, but Dari runs to the bathroom to throw up. In private, the couple has an argument since Rockl thinks this is a miracle while Dari believes the boy isn't the real Mikuel and even thinks he's dangerous.
He remembers how Mikuel set fire to his school and how Rockal lied to protect him. At the clinic, young Gunhild is discharged and she decides she'll stay at the hotel. Older Gunhild calls Bjorn to check on him and assures him she'll be home soon. After the call, Bujornne looks for an old picture of Gunhild and Thor and gets an idea.
Then both Gunhilds visit Thor at the same time. Young Gunhild mentions the time Asa walked in on her father and her getting naughty and old Gunhild angrily rushes out of the room. Thor follows her to assure her he never told the detail to anyone. It turns out that old Gunhild and Thor had an affair back in the day and Asa caught them red-handed.
Old Gunhild still doesn't understand how a random woman knows about their life and leaves. Thor tries to confront young Gunnhild, who insists she's the woman Thor had an affair with. She looks so much like the Gunhild he dated that he brings her to his bed so they can nap together. Determined to find an explanation for what's happening, Griema drives Asa to the glacier.
Asa notices that Griema is taking medicine for her anxiety just like their mother. The duo reaches the abandoned building and sees the cracked window with the blood, concluding someone tried to get in. Next, they notice a raised floor plank and remove it to find some clothes covered in ash. Since they can't pull it out, they decide to dig outside the building until they can reach the area underneath.
Asa crawls in first and sees something so terrifying that she rushes out. A curious Griema enters the hole and she's horrified to find Asa's dead body. When she comes out, she stares at the living Asa, wondering what she really is. Soon, Gizla and his team arrive to start an investigation. Asa goes home and is surprised to find Thor and young Gunhild, who just got naughty again.
She runs out after Gunhild sees her back. Dari hears the news and is worried that Mikuel may be connected to the body. So he calls Gizla to tell him he found another wandering person. When Gizla arrives at the hotel, Rockl sees him through the window and rushes to escape with Mikuel. They climb out the window and use the fire escape to get in the car.
By the time Dari sees them, they're already driving away. So he gets in car to follow them. However, the vehicle stops working in the middle of the road. Griema is called to the police station to testify. When Gizla shows her a picture of the body, she still thinks it looks like Asa. At that moment, the alarm from the observation post rings, but Gizla ignores it, saying it doesn't matter because nobody is there and the alarm malfunctions whenever the wind blows.
However, Griema is worried someone may be hurt and leaves to investigate. On the road, Daria is horrified to see a huge ash storm coming and runs back to town. In the other vehicle, Mikuel tells Rockl that he really hates Dar and hopes he dies. Soon, the ash storm surrounds them, so Rockl stops the car to wait it out. She asks Mikuel if the school fire had truly been an accident, and he says it was, but he also admits he'd been happy because he hoped the other students would burn.
It turns out the other kids used to harass Mikuel, who even considered self-deing. He says he won't play nice anymore, and if Dari locks him up again, he'll kill him. Then Mikuel says he has to pee and Rockol lets him leave the car only to drive away as soon as he's out. Old Gunhild visits Thor again and sees that young Gunhild is still around.
She wants to announce something important, but she's interrupted by a strange noise. Thor goes outside and discovers that the peculiar birth is dead. When he goes back inside, an argument ensues because old Gunhild can't believe Thor got naughty with the woman who stole her identity. However, Thor thinks they're the same person in different points in time.
He can't explain it, but he's happy to have his old girlfriend back. At the hotel, Bergrun sees Dari arrive and tells him he should have stayed away from the kid. She explains that the area is full of legends about the changelings, which are substitutes left by supernatural beings after kidnapping the real person.
Meanwhile, Gizla shows Asa a picture of the body, but Asa doesn't recognize her own face. He keeps asking her questions, but Asa refuses to answer. Afterward, Asa gets to reunite with Giza's son, Einer, who used to have a thing with her. They leave together and hide an abandoned house where they drink and even kiss.
However, Asa starts feeling uncomfortable and decides to leave. She ends up in the clinic where she cries until the doctor lets her spend the night there. Griema is crossing the storm when suddenly her car stops working. She checks the engine and notices a shadow moving in the observation post. So, she heads there. When she enters the kitchen, she discovers a woman who looks just like her covered in ash.
When the storm calms down, Griema takes her clone home and tries asking questions, but the other her doesn't have answers. In the meantime, Rockl regrets her decision and goes back for Mikuel, but she can't find him. A couple of locals end up finding Mikuel instead, and they call the hotel to warn Dari. He promises he'll pick him, and after hanging up, Rockl comes back.
She cries as she admits what she did. So Dari assures her that Mikuel is fine. While waiting for Dari, the couple chats with Mikuel, who tells them all the supposedly horrible things Dari did to him. By the time Dari and Rockl arrive, the couple is leaving with Mikuel because they think he's being abused by his parents. They plan to take the boy to the police.
The couple drives off, but Mikuel feels uncomfortable and opens the car door to escape. The woman catches him just in time and makes him sit, so Mikuel responds by slashing her neck with the utility knife. Her husband freaks out when he notices and loses control of the car, which moves off the road and loses a tire.
This makes it roll down the hill and the husband hits his head on the window. Mikuel survives the crash and watches the man die right in front of him. In town, Geese gets home and is shocked to discover a healthy duplicate of Magneia. He rushes to the bedroom and finds his sick wife in bed looking terrified. Seeing his healthy wife still makes him happy, though, and he even cries.
Young Magne tries to feed the old one, who angrily knocks the smoothie out of her hand. When young Magneia changes her now stained clothes, Gizla notices the ash on her back and old Magneia writes something in his notebook. When Gizla isn't looking, young Magneia opens the notebook and reads, "She is a devil. Get her out.
" She takes the notebook to old Magneia and asks her to write what she means, but Gizla interrupts them and doesn't let them communicate. A furious Magneia tries to leave to clear her head, but Gizla doesn't want other people to see her, so he captures her and locks her up in the basement. Sometime later, Thor notices that there's blood on Gunhild's clothes and immediately takes her to the clinic.
The doctor tells him that they will keep her overnight for observation, which is overheard by Asa. At home, new Griema wants to know why she's been kept hidden. At that moment, old Griema gets a call from her team about the accident. So, before going to help, Griema leaves a note for her husband about her clone.
When Kyran gets home, he reads, "I had to rush out, this woman isn't me. I'll explain later." Then, New Griema surprises Karan with a hug. Moments later, Rockl is still looking for her son and finds the rescue team investigating the accident. She tells them that Mikuel had been with the dead couple, but nobody has seen the kid.
Rockl shares the story of how Mikuel died and came back, but it makes Gizla nervous, so he says she's delusional and leaves. Then Rockl takes Griema to meet Dari so she can share what happened with her sister and Gunhild. She even confesses she has a clone, too. Dari thinks it's all connected to Katla. At the clinic, Thor visits Gunnhild and kisses her forehead, which annoys a spying Asa.
When Gunnhild wakes up, Asa asks her if she loves Thor, and Gunhild says she never loved anyone so much. Asa admits she never saw him so happy before and Gunhild comforts her. Gizla picks up Magne's medication and the doctor reminds him that she doesn't have much time left. On his way home, Gizla stops at a store to pick up some herbal medicine.
At home, he replaces the real medicine with the herbal supplements before giving them to his wife. Then, he takes some food to the clone in the basement, asking her to be patient because they'll be together soon. After Giza goes upstairs, Magneia breaks the handle of a spoon and uses the remaining metal to break into an emergency box where she finds a hammer.
The next time, Gizla comes downstairs. He finds Magneia gone and the window broken. Later, Thor receives a surprise visit from Bjornne, who just arrived on Vic. Bjornne explains that he's Gunhild's son and starts asking lots of questions. Thor quickly realizes this young man is his son and uses a metaphor about cat rescue to say how much he regrets not being in Bjornne's life.
Then Thor calls Gunhild and she comes to pick her son up. She reveals that Thor always knew she was pregnant, but before she left, she told him she would terminate it. Unfortunately, she waited past the legal amount of months to do the procedure and had to go to a shady witch. However, the procedure made her sick and hurt the fetus, so she thinks her mistake made Bjorn disabled.
When Griema gets home, she finds lots of furniture outside. She rushes into the house to discover the clone redecorating. A furious Griema goes to complain to her husband for letting her do this, but Kran doesn't believe the double story. He thinks he's seen Griema having a personality change because of mental health issues.
Griema returns to the house and can't find her clone. But she gets a call from the police department confirming that the body she found is indeed Asa. While the original Griema rushes to the police station to get the DNA proof she needs, her clone approaches Kyran and starts kissing him, giving him the affection he's been craving for a year.
When Griema comes home, she finds her husband and her clone getting naughty and sharing words of love. Determined to get answers, Dari goes with AA and Leaf to the crevice to investigate. He climbs all the way to the bottom and enters a very dark tunnel. After walking for a while, he notices a piece of strange rock falling from a moving wall.
He takes a closer look and is shocked to find dozens of bodies covered in ash hiding among the rocks. When the group returns to the observation post, Dari doesn't tell the others what he saw and concentrates on studying the samples he's brought. He mixes the ashes with some liquid, and he's shocked to watch them move on the dish.
After a few more tests, Dari calls Rockl, A, and Leaf to tell them he's found a meteorite. It's been buried under the volcano for thousands of years and the eruption has spread tiny meteorite pieces all over the area. Aa fears that the meteorite may be radioactive and thinks everyone should leave. In the evening, Griema finds Asa and shows her the DNA tests that confirm the body is her real sister.
Asa wonders what she is and realizes she feels like she has no purpose because technically she doesn't exist anymore. A crying Asa tells Griema how much she loves her and asks her not to stop her. Then she walks into the sea to selfdelete, triggering a memory of how they saw their mother do the same. This gives Griema closure, implying the changeling was created to help her move on.
The volcano continues to eject dangerous amounts of ash and the bodies in the tunnel stir. Griema spends the night in her car while Kartan loves how nicer the clone is. After a visit to the clinic, Thor goes looking for Gunnhill to share some important information. It turns out that young Gunhild's baby is also disabled because it's always been a genetic defect.
Old Gunhild's procedure had nothing to do with it. Afterward, Gunnhill tells Bjornne that they're going home. However, Bjornne wants to stay to get to know his father better. Then Gunnhill goes to the clinic to visit her younger self, but the bed is empty and the doctors don't know what happened. Gunhild then decides to let down her hair like she used to, indicating this changeling appeared to help her move on from her guilt regarding Bjornne's disability.
Now that Gunhild is better, the young one disappeared. At the same time, Thor tells Griema that she has a half brother. In return, Griema tells him that Asa was fake and she's gone. Meanwhile, Mikuel has sneaked into the back of a truck that takes him back to town. He runs to the hotel to find his parents.
They ask him about the accident and Mikuel admits he killed the woman, but they don't do anything. The family leaves together in the car and Dari notices that Mikuel still has the knife, but the boy refuses to hand it over until Rockl asks nicely. The family stops at the beach, so Mikuel can play for a while. Dari theorizes that the meteorite created illusions based on the strongest emotions of the people who came near it.
He thinks Mikuel is a manifestation of how Dari destroyed his marriage and blamed the boy's death for it. Both parents cry as they agree that this Mikuel can never replace the real one. Gathering all their inner strength, the couple drags Mikuel into the water to drown him until he disappears. This changeling was created to help them move on from their son's death.
In town, Gizla takes old Magneia out for a ride. He makes a stop at the store where New Magneia spent the night and searches for her with a gun in hand. New Magne panics and runs out to get in the car with her counterpart. Gizla raises his gun, but he doesn't know who to shoot, so the Magneas get to drive away.
A desperate Gizla forces Einer to lend him his car so he can continue the chase. Einer gets worried, so he goes to his parents' home only to find it empty. On the counter, he discovers the medicine switch. He goes to the police station and furiously starts beating up his father. When Gizla tries to say that it was God's will, Einer hits him in the head with a religious figurine and announces he's dead to him.
It seems the changeling didn't come to help Gizla, but to rescue Magneia from her husband. When Griema goes home, she notices the house is looking much nicer and livelier thanks to the clone's efforts. She yells at her copy for barging into her life and taking Karton from her. New Griema points out that Asa became Griema's mother figure after her real mom died, which is why her disappearance hit Griema so hard.
Their conversation is interrupted by Karton, who only sees and talks to the copy while ignoring the real Griema as if she wasn't even there. After lots of thinking, Griema decides to grab the farm gun and just one bullet so she and her copy can play the deadly Russian game. Several rounds pass without anyone getting hurt, but eventually the bullet chooses one of them and kills her.
It seems this changeling was born from Kartton's need to have a happy wife again instead of a depressed shell of a woman. Sometime later, Griema plays the piano again after years of not touching it. Thor, Bujorn, and Karan listen to her like a happy family. Under the volcano, the bodies finish waking up and come out of the tunnel.