Before the main story begins, Catherine, whose real name is Ahn Si-yeong, had already been living in Australia for some time on a working holiday visa, staying in a share house in the Ballarat area alongside a handful of other Korean workers who all held jobs at the same meat-processing plant, Meatville. Within that house Catherine had become something like its emotional center: she cooked for everyone, she was the one people went to with their problems, and she was generally looked up to as an older-sister figure by nearly all of the housemates. The one relationship of hers that puzzled everyone was her romance with Hans, the young man who effectively ran the share house, because his personality never seemed to match hers and people openly wondered what she saw in him. At some point during her stay, Catherine noticed that Hans had started doing drugs. He'd grown close to a group of Taiwanese coworkers and picked up the habit from spending time with them. She reported this to their workplace manager, not knowing that the manager was secretly already collaborating with Hans. Not long after, while she was under the influence of drugs Hans had given her, Hans assaulted her in an act of sexual violence so rough it broke her neck, killing her. To cover this up, he told everyone in the house that she had simply decided to leave for Sydney, and life in the house went on without her, though several residents, especially one named Smiliey, who kept texting her without ever hearing back, never quite let go of the sense that something was wrong.

The story proper begins when Catherine's younger brother, twenty-year-old Ahn Si-on, who goes by the English name Zion, arrives in Australia after losing contact with her, determined to track her down. He makes his way to the same share house she had been staying in and moves in with the remaining residents, immediately clashing somewhat with the group's impression of him, since a couple of the housemates find him awkward or slow compared to how sharp and well-liked his sister had been. When Zion asks about Catherine, he's told the same story everyone else was told, that she left for Sydney, but neither her old job nor her old lodging in Ballarat have any record of her, and the more Zion pokes around, the more he becomes convinced that Hans is hiding something and may have killed her.

While Zion's investigation forms the spine of the plot, the webtoon spends considerable time on the private struggles of the other housemates, which turn out to be intertwined with the same rot infecting the house. Mite, whose real name is Jang Gi-seok, has been dating Eenie Meenie (real name Sun Hui-min) since high school, after he rescued her from a sexual assault attempt when she was in her second year; the two have stayed together since, and Mite is protective of her almost to a fault, going so far as to instruct Zion early on to stay away from a Taiwanese coworker named Peter, apparently because he suspects some of the Taiwanese workers, possibly including Hans himself, of being involved with drugs. Into this relationship comes Phillip, whose real name is Jin Hwi-yeong and who joined the share house only after Catherine had already vanished, making him, along with Hans, one of the only two residents who never actually met her. Phillip presents himself at first as a mild, bespectacled, even kindly presence, comforting Eenie Meenie after a fight with Mite, but he is gradually revealed to be a predator hiding in plain sight: he sneaks into Eenie Meenie's room to handle and photograph her belongings without her knowledge, and once he learns that she and Mite have quarreled, he deliberately worsens the rift between them, for instance framing Mite for stealing Eenie Meenie's underwear, when in fact Phillip had stolen it himself and hidden it in Zion's room to shift blame. After successfully driving Mite and Eenie Meenie apart, Phillip joins other housemates in taking Eenie Meenie on a trip to Melbourne to console her, and when she returns to the share house ahead of the others and finds herself alone with him, he rapes her. Throughout all this, Phillip behaves as something close to an underling of Hans's, following his lead, though by the story's end Hans discards and kills him rather than protecting him.

A separate thread follows Smilie, whose real name is Ah-in, a striking young woman who turns out to have a prior, unknown connection to Aaron: the two attended the same university and were in the same band club, with Aaron having joined specifically because he'd seen her playing bass at a festival, but because Smilie dropped out of school and left for Australia right after that performance, the two never actually crossed paths back home and only recognize the connection once they're both in Australia. Smilie's arc turns out to be the darkest thread in the story: not long after arriving in Australia, she was sexually assaulted by someone connected to Meatville, and when Justin, the brother of the plant's owner, learns of the assault, he uses the threat of exposing it as leverage to also rape her himself. After being violated twice, something in Smilie breaks with regard to how she values her own body, and under Justin's direction she begins working as a prostitute. As she grows closer to Aaron, who has been following her and has started to piece together what's happening to her, she tries to quit, and Justin appears to agree to let her go, but secretly sends explicit photos of her to Aaron's phone as a form of psychological control. On seeing them, Smilie tells Justin she wants to go back to sex work, secretly planning instead to attend one of his group encounters and poison him, a plan that fails when she's discovered, and Justin nearly kills her with a gunshot to the head before Aaron, who has followed her, arrives just in time to save her. Aaron and Smilie then go into hiding together to escape Justin's retaliation, and it's during this time that Aaron discovers that Hans, not Justin, is the person truly responsible for the deepest danger in the house; he tells Smilie, and rather than fleeing to safety herself, Smilie chooses to go back to warn and protect the other housemates, particularly out of concern for how younger, vulnerable people in the house might be treated by Hans. Aaron wakes to find she's already left to do this and follows after her, and along the way finds Zion, who by this point has been thrown into the water by Hans and left for dead, and rescues him.

That near-death experience for Zion comes from a direct confrontation with Hans, who by then has grown suspicious that Zion is getting close to the truth about Catherine and makes an attempt on his life; Zion survives only because Aaron happens to find him in time. Hans himself is portrayed less as someone with an understandable, sympathetic motive and more as someone who openly describes enjoying the fear and terror he can provoke in other people, a kind of undiluted cruelty for its own sake. Realizing that the housemates as a group are closing in on the truth of what happened to Catherine, Hans decides to eliminate the threat entirely and formulates a plan to lure everyone into the house's basement and kill them all at once. The plan falls apart for several converging reasons: some housemates manage to escape the basement, others arrive back at the house at the wrong moment for Hans's timing, and the group starts fighting back rather than complying.

The story's climax takes place back at the share house, where the police have been called after neighbors or housemates report what's happening. Hans, cornered, grabs Zion and holds him hostage in front of the arriving officers, insisting to them that he isn't some calculating criminal trying to rack up a body count during an escape attempt; he simply wants to kill this one more person. He raises his gun at Zion and pulls the trigger, but during the earlier struggle inside the house the guns had gotten swapped without Hans realizing it, so the weapon in his hand is empty. The moment he fires it anyway, the watching police open fire and kill him.

In the aftermath, with Hans dead and Catherine's murder now understood by everyone who cared about her, the survivors scatter into their own futures: Aaron, once his working holiday concludes, ends up enlisting in the military back home. Time is shown jumping ahead roughly five years, by which point Zion has changed his appearance, now wearing his hair short, apparently having moved on with his life in the wake of everything that happened.

There is also a companion side story that runs somewhat parallel to all of this, centered on a different Korean working-holiday worker named Jane, whose real name is Do Jae-in. Jane works cleaning hotel rooms and at a Korean restaurant, and over the course of her arc she has her own repeated, unsettling run-ins with Phillip, who secretly takes photographs of her without her knowledge; when she eventually catches him doing this, he's fired from wherever he was working alongside her. Rattled by an incident in which two masked men appear to be pursuing her with intent to harm her, Jane considers going back to Korea but ultimately decides instead to leave Sydney for a different region of Australia, eventually finding farm work harvesting onions. There she becomes close to a Korean coworker named John, but after John is fired by the farm's owner, Jane chooses to leave with him rather than stay behind, and the two escape together by car while being pursued, during which their car collides with another vehicle carrying, as it turns out, Hans and Catherine, from a point in time before Catherine's death. It's later revealed that the crash happened because of a cruel game Hans was playing, deliberately speeding after Catherine admitted the speed frightened her, purely because he enjoys hearing people say they're scared of him; this is one of the ways the side story fills in just how disturbing Hans's relationship with Catherine already was before the events of the main story. Jane eventually receives an apology from Catherine over the accident, and remarks to herself in disbelief at how unsettling Hans looks up close. Later in the side story, Jane runs into Zion at a point when he's writing down possible English names for himself, and it's Jane who suggests the name "Zion" to him, meaning her side story quietly explains the origin of the protagonist's nickname. Jane and John grow close enough that it seems like they might end up together, but John ultimately develops feelings for another character, Robin, and Jane and John's relationship ends as a result. The side story closes with Jane meeting Zion again once all of the main story's events have concluded, and finally returning home to Korea.