A flashback reveals that Oh Si-eun's name was removed from the Diamond Club because her family went bankrupt. Since then, she's no longer one of the six wealthiest students at Cheongdam and has been relegated to the blackboard. Other students mock her, leading Si-eun to angrily confront one of them. However, Je-na intervenes, slapping Si-eun. Si-eun questions why Je-na would treat her this way after they were once close friends and Si-eun did so much for Je-na.

Je-na tells Si-eun she wants nothing to do with her anymore and demands that Si-eun stays away from her. Presently, Je-na encounters Si-eun and questions her motives for associating with Hye-in. Si-eun gives a false excuse, but Je-na sees through it and warns Si-eun to stop whatever she's planning.

At this point, Si-eun drops her facade and reveals she knows about Je-na's dad's affair with their former English teacher, who is now pregnant with a son. Si-eun taunts Je-na, predicting her downfall in the school. They argue, mentioning something about Si-eun being responsible for Je-na's older brother's death. Si-eun leaves while Je-na is left in crisis, contemplating how her position at school might be affected.

Meanwhile, Do-eon observes Je-na from afar, certain that she is behind Hae-in's accident. He recalls how Je-na was indifferent to what happened to Hae-in and his father's advice when Hee-seo asked him to be cautious of his friends.

Si-eun enters the art room where Hye-in confronts her. Si-eun admits to threatening Hye-in, claiming that because Hye-in was present at the scene where the girl pushed Hae-in off the roof, she needs to blame Je-na for the attack. Si-eun gives Hye-in seven days to publicly accuse Je-na of Hae-in's accident; otherwise, she'll release secretly recorded footage of Hye-in online. Si-eun reveals that Duk-min frequently runs cameras in the Diamond Club and has recorded numerous videos of students dating and changing clothes. She bought the video from Duk-min and threatens to publish it online if Hye-in doesn't expose Je-na. Do-eon goes to the prefect room and meets Woo-jin, Yul-hee, and Je-na there. He tells them that he will bring Hye-in with him to their anniversary party. Je-na gets angry, unable to understand why Do-eon sees something in lower-class people like Hae-in and Hye-in.

A flashback shows Hae-in talking to Je-na on the rooftop before her accident. Hae-in realizes that Professor Ha is pregnant with Mr. Baek's child and claims to have seen Je-na's driver late at night bringing her there. She uses this information to blackmail Je-na and ask for something. However, in the present, Je-na is still not ready to tell her friends about this.

Je-na then visits her mother in the hospital. Her mother reminisces about their good memories together, but on the way out, Je-na overhears her driver telling someone that shareholders will soon reconsider Je-na's mother's shares because Mr. Baek will soon have a son. Hye-in walks home and receives a message from Si-eun reminding her of their agreement. She sees a poster asking for witnesses from Hae-in's mom. Overwhelmed with guilt, she cries in the middle of the street.

Je-na sees Hye-in crying and stops her car. She questions Hye-in, still acting cold, but when she sees Hye-in crying and mentioning Hae-in, Je-na says that Hae-in is not as innocent as she appears, and Hye-in should be strong because giving up and being sad is not like her at all.

Just then, Si-eun calls, and at the same time, Je-na warns Hye-in to be careful with Si-eun. Afterward, she tells the driver to move on.

Feeling empowered, Hye-in turns off Si-eun's call and calls Do-eon, agreeing to help him.

The next day, Do-eon and Hye-in go to the Diamond Club room and kick Woo-jin out, claiming they are a couple and want to use the room for themselves. Once Woo-jin leaves, they start searching for Duk-min's video box. Finally, they manage to open the drawer full of USBs containing Duk-min's recorded videos. Meanwhile, So-mang is beating Duk-min and forcing him to delete all videos from his cloud drive. So-mang warns Duk-min that if he ever releases any videos online, she will release his videos. Hye-in and Do-eon leave the room with a box full of USBs.

Meanwhile, Professor Ha visits Mr. Baek and is shocked to see Je-na there. Je-na pretends to be cheerful and calls Professor Ha "Mom." Professor Ha is terrified by this sudden change.

Professor Ha follows Je-na out of the office and wonders what she's doing with her "good daughter" act. Je-na reveals that she's tired of waiting for someone to inherit her mother's fortune and declares that she will intervene to prevent Professor Ha's son from becoming the heir to the Hanmyeong conglomerate.

Meanwhile, at her home, Hye-in opens the USB named "hae in" and finds a video of hae in making out with Woo-jin in the prefect room.