In the fifth episode of "Mad Concrete Dreams," the story picks up as Su-jong and Kim-su grapple with the aftermath of their actions against Dong-gi in the bathroom. Su-jong is visibly shaken, realizing that the consequences of their kidnapping plan have escalated far beyond his expectations. They lock Dong-gi up in the underground freezer storage room, where Kim-sun, with her nursing experience, tends to his wounds with a surprising level of composure.
As she calmly works on the wound and helps Su-jong clean up the scene, he is both impressed and puzzled by her behavior. He brings up the affair with Hwal-sung, but Kim-sun stops him, reminding him that this is not the right time to discuss it. Both of them have made mistakes and need to focus on dealing with the urgent problem at hand.
At the police station, Ju-ran continues her investigation into Gyun's death, leading her to the Changsim Building. She goes into the demolished building and discovers Jeong Chang-su's body under the ruins. She reports the case to Yong-hoon, seeking authorization to investigate Real Capital and Sang-ho, but he denies her request.
Meanwhile, Yi-gyeong still feels that Hwal-sung is hiding something from her. She goes through his phone after picking it up from the police station and learns about the loans he took from Loan Heaven and paid them all back. At the hospital, she uses his fingerprint to unlock his phone and discovers messages in which he's flirting with other women. She also finds a hidden Instagram account with pictures from the trip he took with Kim-sun and the messages they exchanged. In all the pictures, Kim-sun's face is hidden, so she doesn't realize she is the woman in the affair.
Back at the freezer, Su-jong is still hung up on the affair and continues to waver. Kim-sun asks a nurse friend for blood bags, and Su-jong donates blood to stabilize Dong-gi's condition. The scene is filled with tension as both characters struggle to deal with their emotions and the consequences of their actions.
Su-jong wonders what will happen if he doesn't agree to their terms, and Kim-sun doesn't hesitate to inform him that he'll have to choose between protecting either their family or Dong-gi. Later that night, Su-jong searches for ways to painlessly kill someone. Meanwhile, Yo-na and Dr. Jang push the agenda of their mysterious boss's interest in the Sejeong-ro redevelopment project by helping Sang-ho take care of his assistant. It turns out he was doing something that betrayed Sang-ho, so he needed to disappear.
In the freezer, Su-jong chooses to negotiate and apologizes to Dong-gi to reach an agreement. Dong-gi knows too much about the kidnapping and the money, though, so he demands one billion won in exchange for his silence and pressures Su-jong not to make a bad choice that would disappoint his daughter.
Just then, Su-jong gets a call from Kim-sun about Yang-ja and Yi-gyeong coming for a meeting to discuss the sale of the building. Yang-ja offers 30% above the building's market price. Although Su-jong knows about the redevelopment, he plays the fool and instead uses the fact that many people want to buy it to hold onto it longer. Yang-ja storms out, calling them fools for not realizing the dangers they are dealing with.
Kim-sun and Su-jong agree to pay up Dong-gi, but to ensure he keeps his end of the deal, they record a video of him confessing to being an accomplice and vowing to keep quiet. Before they could let him go, Yi-gyeong showed up at the building looking for Kim-sun. An altercation breaks out when Dong-gi attacks Su-jong, who cries out for help. No one hears him, though, as Kim-sun leads Yi-gyeong to the roof for a private talk.
She unloads her anger on Hwal-sung's betrayal, and Kim-sun offers her a pep talk, reminding her that people are never satisfied with what they have and often seek fulfillment elsewhere. Meanwhile, Dong-gi and Su-jong's fight in the storage room continues. Dong-gi manages to reach for the keys and uncuffs himself, subduing Su-jong before Kim-sun arrives and knocks him off Su-jong.
Elsewhere, Yang-ja seeks Mr. Kim's help to force Su-jong out of the Seyun building. She wants him to replicate a tactic they've used before by creating a building defect in the Seyun building. Mr. Kim refuses to get his hands dirty, so he only lends her the tools.
As Su-jong and Kim-sun vow to stick together until the end, Dong-gi is trying to stop the bleeding on his broken fingers. At the same time, Yang-ja sets her plan in motion by cutting the water pipes and starts flooding the building.
She opens the freezer where Dong-gi is still locked up, and he mistakes her for his kidnappers and attacks her. The episode ends with Dong-gi fleeing the scene after he realizes that the person he attacked is neither Kim-sun nor Su-jong, leaving Yang-ja bleeding and struggling to breathe in the freezer.
