In the opening episode of Concrete Market, the scene unfolds with two lifelong friends, Choi Hee-ro and Han Se-jeong, sharing a heartfelt moment as they tie each other's hair atop a rooftop. As the day unfolds normally at the supermarket, the world suddenly shudders to a halt with the blaring of alarms, followed by a devastating earthquake that brings everything crashing down.
The post-apocalyptic landscape reveals a new and harsh reality where survival becomes the paramount concern. A woman, digging through the debris, uncovers canned food, which she exchanges for a precious commodity – water. Another encounter shows a brutal exchange where a woman kills a man for a can of food, taking it to the solitary building still standing, where she trades it for access to running water. This building, controlled by Park Sang-yong, becomes the hub of a makeshift market known as Hwanggung Market, where people barter for their basic needs.
Canned foods emerge as the primary medium of exchange in this desolate world. A box of these cans can secure anything from running water in the building to rent payments and even licenses for businesspeople operating stalls around the building. All transactions are brought to Sang-yong's ninth-floor residence.
Hee-ro embarks on a treacherous journey through the wastelands, collecting empty cans of canned foods with the sole aim of reaching Hwanggung Market. She has heard rumors that anything is possible there, as long as one has canned foods. Upon presenting her duffel bag filled with cans, she is granted entry with a stern warning: leave immediately when the alarms sound. She is directed to the eighth floor, where people with nothing to sell reside. Any presence outside after market hours is considered a thief and dealt with immediately.
As she explores the market, Hee-ro passes by a man preaching about the end of days. A bonfire captures her attention, where people are ritualistically burning money and books. Unable to resist, she steals a book and continues her journey through the market. The preacher's attempt to flee with two cans of food is quickly thwarted, adding another layer of tension to the already chaotic scene.
However, he runs into Kim Tae-jin and his boys, who control this side of the market under Sang-yong's orders. Tae-jin nails the two cans to the preacher's hands, leaving him groaning in pain as he starts collecting payments from the merchants. Tae-jin discovers one of the business rooms closed, where the merchants had committed suicide inside. As his men concentrate on cleaning up the bodies, they leave the sack of collected canned foods unattended, and Hee-ro steals it.
Before that, she had helped the preacher by removing the nails and bandaging his hands, so he called her the good Samaritan. When Tae-jin asks him who took their goods, he says it was someone limping and carrying a duffel bag. While Tae-jin and his men are busy looking around the market for a person carrying their sack, Hee-ro finds a place on the second floor, dumps the empty cans, and puts the food in her duffel bag. She also removes the bandage from her leg, which has no wounds. She tries to leave the market, but Tae-jin closes the gate, preventing anyone from leaving.
She scrambles for a place to hide, but Tae-jin's men are all over the place. She hides the bag in one of the cars and looks for a rope. Before she can climb over the wall, she sees Se-jeong on the stairs. She hides the bag and heads back to the building.
Meanwhile, Se-jeong is with Sang-yong. She exchanges sex for drugs, but this time Sang-yang refuses to give her the drugs and invites her for dinner instead. She has no choice but to head out, and she runs into Tae-jin and Park Cheol-min at the door. They have come to report on business in their areas. Tae-jin is told to step up his control, or Sang-yong will give his area to Cheol-min, who is doing a better job.
Later, Se-jeong is bullied at the line to get water rations. She receives preferential treatment due to her relationship with Sang-yong, which has angered many people. She gets the water for free, but Cheol-min trips her and spills all the water. Hee-ro follows her outdoors while observing from the sidelines.
Hee-ro's heart swells with a myriad of emotions as she discovers that it's her dear friend Se-jeong, and her tears uncontrollably spill over. Se-jeong leads her to the rooftop, where a small garden of blooming flowers greets them. Hee-ro's gaze lingers on the needle marks, and Se-jeong opens up about her connection with Sang-yong.
Hee-ro urges her to leave, but Se-jeong insists that living at the market isn't as bad as it seems and tries to persuade her to stay. Just then, Sang-yong's warning call disrupts the moment, and Hee-ro has to hastily leave before the market shuts down. Later in the night, Se-jeong arrives at Sang-yong's house for their dinner date.
Hee-ro hides in a car that night, watching as Tae-jin hides canned food in another vehicle. Tae-jin catches a glimpse of her shadow and approaches to investigate. Before he could reach her, a deafening crash echoes through the night, reminding him of the earthquake's traumatic day. Hee-ro steps out of the shadows to investigate. She witnesses Se-jeong's final breath as she sadly falls to her death.
