Park Junmo's insistence in seeking revenge for Taeho's death gains him an in with the Gangnam Union. Eventually, Yu Euijeong finds out about his undercover mission.

Yu Euijeong and Jung Gicheul meet again for the first time since high school.

Park Junmo, as Kwon Seungho, tells the Gangnam Union that he's Taeho's cousin and that he's here to avenge Taeho's death, pretending to be disgusted by the fact that they, who claim to be friends of Taeho, haven't yet avenged him. Jung Gicheul gives Junmo his business card and offers to meet with him.

Gicheul and Jungbae go to Taeho's father's house to follow up on "Seungho," and Taeho's father—who had previously been contacted by the police—corroborates Junmo's story.

Junmo shows up to the Gangnam Union HQ and Gicheul tries to pay him off, thinking Junmo is running a scam using Taeho's name, but Junmo rejects the money and insults Gicheul and his men again. Gicheul threatens to start a fight, and Junmo is up for it, so a number of the Gangnam Union fight him. Junmo, who fights well and extraordinarily viciously, ends up victorious.

Junmo gives Taeho's watch to Gicheul, vowing to gain revenge for Taeho's death.

Hong Heesung wants to bring Junmo into the gang, but Choi Jungbae is against it, finding Junmo suspicious.

At night, Oh Kyungjin and Jung Byungwoo are walking through Gangnam Union territory when they see Junmo handing out "murder suspect" flyers about Sergeant Jang, the man who killed Taeho.

BUSAN, SOUTH KOREA

Hong Heesung shows up with the money Gangnam Union owes to Song Donghyuk. Afterward, he walks through the dockyards to meet with Hando, who used to be one of Sergeant Jang's men. Heesung claims to want to betray Gicheul, saying that Gicheul's wealth has changed him and not for the better. Heesung proposes that Hando pull together the Busan gang again and take down Gangnam Union.

Junmo leaves a message to Euijeong through a payphone, claiming to be in Daegu chasing after a murder suspect.

At Sikgaek, Gicheul, Jungbae, and Chief Seo are eating. Heesung joins them and asks Chief Seo to pour him a drink.

Back in Busan, Hando approaches Song Donghyuk with the idea of pulling together the old Busan gang and taking down Gicheul and his men.

In the undercover operation HQ, Junmo throws a tennis ball at a picture of Gicheul as he idly thinks about the case. He's interrupted by a page from Gicheul himself, asking to meet.

Outside the unopened Taeho Rock Cafe, Heesung drives by with Hando and some of his men. Heesung, Hando, and the men plan an ambush at the party Gicheul is going to host there that night. Heesung says he'll hide weapons under the bar so they can easily grab them, but then asks that they don't hurt the men in Gangnam Union too much, who are his friends and brothers. Hando and his men think this is hilarious.

At night, Junmo walks into the unopened Taeho Rock Cafe while Seok Dohyung watches from inside his car. Gicheul is waiting for Junmo inside. He claims they're having a party for Taeho that night, and asks Junmo to give up revenge and join his gang. Junmo pretends to be unconvinced, but just then Hando, Heesung, and the Busan gang show up. Junmo asks who they are, and Gicheul explains that Sergeant Jang had killed Taeho and these are his men. Hando is ecstatic for a moment, but then learns that Heesung did not actually hide any weapons for them behind a bar—Heesung's apparent betrayal was all a trap. A fight breaks out, during which Gicheul watches Junmo's actions closely. Outside, Dohyung, who has watched men go into the unopened Taeho Rock Cafe, is worried and considers calling for backup, but refrains.

The rest of the Gangnam Union arrive as reinforcements, and the fight starts up again. Gangnam Union wins soundly. Junmo beats up Hando with a metal baseball bat, but is dragged away before he can do too much damage. Gicheul gives Hando the choice of death or leaving in disgrace. Chief Seo breaks Hando's leg with a hammer, and then Hando and his men stumble out of the unopened Taeho Rock Cafe while the Gangnam Union men insult them and tell them to stay out of Gangnam. From his position in his car, Dohyung takes pictures of their exit.

Gicheul gets a call from Song Donghyuk and says that, since Song Donghyuk let the Busan gang move against the Gangnam Union, he will no longer give money to Song Donghyuk. Song Donghyuk orders his men to find Jung Gicheul and kill him.

Gicheul leads Junmo and the Gangnam Union outside, where he shows the Taeho Rock Cafe sign now lit up, and explains that he made this in Taeho's memory. He gives the watch back to Junmo, asking him to make Taeho's dream come true, and then reveals that he had killed Sergeant Jang in anger at Taeho's death.

In the morning, Junmo meets with the Gangnam Union in their HQ, introducing himself formally as Kwon Seungho, and is accepted into the gang. At night, the entire gang walks dramatically through their section of Gangnam.

Park Junmo and Bae Yongdae, the two most junior members of the gang, are now out on patrol from 5 at night to 5 in the morning in Nonhyeon-dong and Yeoksam-dong. Junmo asks why Yongdae uses honorifics with him, and Yongdae reveals that he's a huge fan of Junmo's fighting skills. The two then patrol for some time, while Dohyung drives through, keeping an eye on Junmo from inside his car. Junmo asks how long they'll be the lowest-ranking members, and Yongdae answers that it's probably until new members join.

In the undercover operation HQ, Junmo and Dohyung have a short exchange and Junmo tries to catch some sleep on the couch.

Junmo and Yongdae continue to patrol. Junmo asks whether the gang sells anything other than what they officially sell, but Yongdae doesn't know anything.

SEOUL METROPOLITAN POLICE AGENCY, SOUTH KOREA

Euijeong talks to a suspect named Cha Bongju, being sweet and playing good cop.

In Junmo's apartment, Junmo asks Yongdae why he's moved in with him, and Yongdae explains he used to live with his parents but his parents moved away.

Euijeong calls Junmo's colleagues in Euemseong, since she hasn't heard from Junmo since yesterday; she learns that they think Junmo's taken a sick leave because of his "asthma." She leaves a message for Junmo asking to meet, and they meet at an eatery. Euijeong is angry at Junmo, suspecting that he might be cheating on her, so Junmo explains that he's gone undercover in a gang. At that moment, Gicheul and his men walk in. There are awkward introductions, made more awkward by the fact that Gicheul and Euijeong knew each other back in high school, Jungbae and Heesung also remember her, and Gicheul knows she's a cop. Junmo claims that he knows Euijeong from being in the same Taekwondo club in elementary school.

The gang leaves with Junmo, and they beat him up in the underground car park, asking how he's come to be in contact with a cop. Junmo claims that he used to escape to her house when his father got high and beat him. He says that Euijeong is the one who contacted him, because his father's being held in the SMPA.

Once they all drive away, Euijeong makes a call on her phone, asking if the person on the other end is also involved in this meth investigation.

In the car, Heesung and Jungbae talk to Junmo about their increased suspicion of him, but Gicheul is distracted with thoughts of Euijeong. He takes his cross necklace out from under his shirt and holds it as Heesung and Jungbae turn to reminiscing about Euijeong, claiming that she was Gicheul's first love. Suddenly, Junmo catches sight of the necklace and remembers that he had seen a matching necklace in Euijeong's jewelry box in her childhood home.