As Yi-hyun and Sae-bom come down from doing laundry on the roof, they come across Moon-hee and Se-kyu unsuccessfully trying to convince Young-ok to let them use an empty apartment on the 11th floor. Being on the second floor, they worry they’ll be in danger again if more zombies invade.
Young-ok isn’t happy when they turn to Sae-bom and Yi-hyun for permission instead. Sae-bom suggests they put it to the group. Hae-sung concurs with Young-ok that using the apartment would legally constitute trespassing, which proves a nice excuse for the others to suggest the couple stay in 201.
Hak-je doesn’t want to be the bottom-most resident first in line for the zombies, and Joo-hyung says the residents would feel safer with the cleaning couple acting as “guard dogs.” Wow. Strangely, Andrew looks over at Joon-hyung and smiles behind his mask.
Once everyone leaves, Hyun-kyung asks Sae-bom and Yi-hyun for a word. She tells them about Soo-min contacting her and wonders if it’s possible he isn’t infected. Sae-bom looks at her own scratch and says they can hope.
That night, it rains as Yi-hyun predicted (his injured knee gives him warning), so he and Sae-bom head up to the roof to put out water containers. They’re startled when the sleeping Jung-kook yells at Satan to get back while clutching a cross. Yi-hyun sighs at his sudden religious turn.
In 602, So-yoon suggests collecting rainwater, but Hae-sun refuses to drink anything not filtered. Meanwhile, Hyun-kyung worries about Soo-min and goes down to the lobby. Out the window, she spots him and calls him over. He’s hesitant to come near, but she begs him not to run away. Is he truly infected? Soo-min isn’t sure, but he does feel strange.
The next morning, Sae-bom and Yi-hyun find Andrew drinking from one of their water containers. Yi-hyun is miffed, but Sae-bom says it’s fine. She takes a swig of rainwater from a container, despite Yi-hyun’s protests that it’s unsanitary.
Se-hoon comes up to collect his own container and invites Sae-bom to use his water purification tablets. “Tell your husband in advance, though,” he quips drily. Ha. Sae-bom doubts a guy who purifies his water would take Next, but Yi-hyun is still leery. Andrew eavesdrops with interest.
Downstairs, Yi-hyun and Sae-bom run into the cleaning ajumma. She shows them the bloody towel she found in a trash bag between the third and fourth floor while cleaning. (Young-ok is still making her clean to keep her salary.)
Their first stop is Hyun-kyung’s, but she vehemently assures them it’s not her. She even rolls up her sleeves and exposes her neck to prove she’s injury free. Yi-hyun then drags Jung-kook (and his gun) to go looking for Soo-min, assuming the blood is his.
They find a lunchbox in the garage, but Jung-kook holds Yi-hyun back from going further to investigate. There’s nothing they can do anyway, and Jung-kook is determined to get back to his wife safely – her breast cancer seems to be back.
That night, Yi-hyun tells Sae-bom that Jung-kook is right that there’s nothing more they can do. Right as they agree to lay low, they hear a thudding upstairs.
Elsewhere, Ji-soo reports that a test subject is showing a positive reaction to the treatment. Tae-seok rushes in to see Seung-young (He’s alive!) looking much better. His thirst is gone, but he does now enjoy eating meat when he used to be vegetarian. Tae-seok orders Ji-soo to continue analyzing Sae-bom’s blood in secret but report the success of the clinical trial to the higherups.
The final day before end of quarantine, Hyun-kyung sneaks up to 1102 with a basket. (Oh no, is she keeping Soo-min in there?) When she comes out, Yi-hyun and Sae-bom are waiting for her. Under pressure, she admits her brother is in there and reluctantly lets them in.
Yi-hyun asks about the lunchbox, and Soo-min reveals it was Joo-hyung who gave it to him. (Oh great, it’s probably laced with Next.) Soo-min refused his offer of coming inside, though, because he was afraid of biting people.
Yi-hyun is angry at the siblings, but Sae-bom takes a softer approach. They instruct Hyun-kyung and Soo-min to stay inside. Once the lockdown is lifted, they’ll bring back medical help.
In 302, Dong-hyun pulls Bo-ram aside and confesses he thinks his mom is infected. He knows she has a wound, and then there were those zombie thudding sounds last night. Bo-ram scoffs when he’s only concerned about them getting infected and tells him to be good to his parents.
That night, Sae-bom shares she’ll first visit her mom when the lockdown is lifted tomorrow. Yi-hyun’s parents are in the US, so they assume they’re okay. Sae-bom wonders if they did the right thing regarding Soo-min. When Yi-hyun notes he seemed okay, Sae-bom recalls Tae-seok saying the thirst is controllable if someone has the will.
The next morning, there’s still no cell or television service. Jung-kook stays home with Seo-yoon while Sae-bom heads down to meet everyone in the gym. When they arrive, there’s a cooler with drinks waiting for them. Oh no, are those the ones Joo-hyung laced?
Joo-hyung comes in and asks if Young-ok provided the refreshments, knowing she’ll take the credit. Only Yi-hyun looks skeptical, especially when Joo-hyung hands him a drink personally.
Yi-hyun and Sae-bom head to the lobby to check on the situation, and he stops her from drinking anything. What if someone put something in it? Thank goodness someone is cautious here. They head to the perimeter, but nothing has changed.
In 302, Dong-hyun hears that thudding again. It’s coming from behind a closed door in the apartment. Before he can investigate, the city alarm blares with an announcement: martial law is being extended indefinitely.
Joo-hyung quickly slips out of the gym as everyone panics. He returns to his apartment to find Hae-sung there with Sang-hee, supposedly for a consultation. It’s obvious something is going on between them, and Joo-hyung eyes them warily. After Hae-sung leaves, Joo-hyung urgently stops Sang-hee from drinking one of his drinks.
In the gym, everyone frets over what to do. Dong-hyun comes running in and rats out his mom. He explains the thudding was her, and she has a wound on her back. Hak-je defends Sung-shil, saying it’s just from psoriasis. Bo-ram jumps in to support his statement, but everyone still wants to check it out.
Hak-je refuses to let anyone in his apartment and instead promises he and Sung-shil will quarantine themselves. Bo-ram throws a disgusted look at Dong-hyun and goes back with Hak-je.
Young-ok says they need to start passing out the supplies in 201 to residents, which starts a fight between her and the cleaning couple. She argues they’re staying for free and should be grateful for what they get. Geez. Yi-hyun and Sae-bom decide they need to do something about Young-ok’s power trip.
Meanwhile, Hak-je sends Bo-ram away for her safety, encouraging her to go see Sae-bom and Yi-hyun for help. Inside, he doesn’t say anything to Sung-shil and acts like everything is normal.
Yi-hyun and Sae-bom show up at Young-ok’s and force their way in. They notice the cheap appliances and lack of furniture, almost as if Young-ok and Woo-chang planned on a temporary stay. Yi-hyun pulls out Young-ok’s water bottle and says he knows she gave it to Seung-beom.
He accuses her of bringing Seung-beom in to support her efforts to become resident rep to “spend public funds and embezzle the profit.” Young-ok is flustered and asks if he has proof. Yi-hyun doesn’t respond, but Sae-bom vows Young-ok will never become the resident rep.
As they leave, they pass Jung-kook who’s coming to pray with Woo-chang. Sae-bom worries he’s getting sucked into a cult, but Yi-hyun argues it’s natural to need someone to lean on. He was like that too after he lost baseball, although religion wasn’t where he turned.
Joo-hyung stops by 201 and wants to buy water for which Se-kyu charges him an exorbitant amount. Se-kyu and Moon-hee make up their minds to extort all the rich people.
Upstairs, while Woo-chang leads Jung-kook in prayer, Young-ok thinks back to the scratch she saw on Sae-bom’s hand. She asks Jung-kook about it, also noting there was something strange with Tae-seok. Jung-kook has the look of someone about to crack.
At home, Yi-hyun goes through the bag of supplies he procured from Ji-soo. He got snacks for Sae-bom and even a military two-way radio. They pack it away when Jung-kook comes in, not wanting to worry him further, but he already looks pretty unsettled.
Privately, he asks Sae-bom about her scratch that isn’t healing. She assures him she’ll let him know if something is wrong. He doesn’t look comforted.
That night, Dong-hyun sneaks back home to swipe food and goes to 201. He begs them to take him in, offering the food and water as a gift. The cleaning ajumma gives him her room in exchange for taking some of the food with her. Only Andrew seems concerned for her. He asks where she’ll go and tells her to be careful since people are getting meaner. She gets emotional when he gifts her an apple.
Meanwhile, Joo-hyung is scheming again and takes Young-ok up to 1102. He happened to see Hyun-kyung bring Soo-min inside, but he only tells Young-ok that something is hidden here. He sends her in while he stays safely in the doorway. She opens the bedroom door and screams.
Yi-hyun and Sae-bom test the radio, but they can’t reach anyone. Sae-bom brings the conversation back to what he said earlier, asking what he relied on after losing baseball. When he honestly admits it was her, she gets embarrassed.
He steps closer to her, looking like he might kiss her. She doesn’t move away. But they’re interrupted by Joo-hyung and Young-ok who asks if they’re the ones who hid Soo-min inside.
Sae-bom and Yi-hyun join Hyun-kyung at 1102 to talk to Soo-min. They head inside cautiously, but Soo-min looks the same as ever. He swears he hasn’t bitten anyone and cries for them to save him so he can see his children again.
They handcuff him in the gym like they did with Seung-beom. He asks them to protect Hyun-kyung and reveals that he wasn’t the one making those thudding noises.
In the hall, Young-ok tries to threaten Yi-hyun and Sae-bom into supporting her as rep, arguing she could get them quarantined for being in contact with Soo-min. She chuckles and says they know Joo-hyung is crazy – they’re too soft to go against him.
Yi-hyun and Sae-bom pay Joo-hyung a visit. He wants them to drink something to prove they aren’t infected and hands them bottled drinks. Yi-hyun insists Joo-hyung do the same and switches his and Joo-hyung’s bottles. Then, they all drink.
In the hall, Woo-chang and Young-ok try to convince Jung-kook he should step up and “create order” by locking up anyone who could be infected.
Sae-bom and Yi-hyun listen to Joo-hyung throwing up in the bathroom. She wonders if they should too and asks how to vomit on purpose. When Joo-hyung comes out, he shows them the Next pills and admits to dosing all the drinks.
His main targets were Sae-bom and Yi-hyun, while the others are a “bonus.” The more patients there are, the faster treatment will develop. Assuming they’re now infected, Joo-hyung tells them to lock themselves away until there’s a treatment or ask Tae-seok for help.
To Sae-bom’s horror, Yi-hyun takes the remaining Next pill Joo-hyung put on the counter and pops it in his mouth. She’s speechless when he says it’s just his digestive meds. He anticipated Joo-hyung’s plan and switched them out.
Sae-bom laughs in appreciation and takes Joo-hyung down when he lunges at Yi-hyun. Now they have evidence from the dashcam of Joo-hyung stealing the pills. They march him out of the apartment and are faced with Jung-kook pointing a gun at them.
Jung-kook can barely look at them as he says that he really can’t get infected. Young-ok backs him up, saying that they need to be quarantined. Sae-bom was scratched, and she and Yi-hyun came into contact with the infected.
Elsewhere, Chairman Choi and his friends happily take the treatment shot. He’s in a good mood and tells Tae-seok to treat his wife, too. Chairman Choi suggests maintaining martial law and the quarantines to decrease the number of infected. Then the demand won’t be as great, and they’ll be rid of the murders.
Tae-seok smiles and agrees it’s better to get rid of problem people “like you all.” Chairman Choi senses trouble and sets the security guard on him, but Tae-seok viciously beats the man down. As the security guard bleeds, the infected all start to turn. Tae-seok remarks they’re helping him gather data.
He lets Ji-soo believe they snuck the treatment out without knowing it failed the second trial. He orders they not be killed but kept alive for testing. Tae-seok sits by his wife’s bedside and holds her hand. When she says she’s thirsty, he cries and tells her they’re almost there.