S Line episodes 3 and 4 recap: Lee Ji-wook discovers chilling truth about himself as he becomes part of the mystery

S Line, starring Lee Soo-hyuk, Arin, Lee Da-hee, and others, released episodes 3 and 4 on July 18, 2025. The drama follows Shin Hyun-heup (Arin), a girl who sees red lines on people's heads. These lines connect to everyone with whom they’ve had physical relationships.

In episode 3, Shin Hyun-heup asked police officer Lee Ji-wook (Lee Soo-hyuk) to investigate a pair of glasses she may have seen at the scene of the incident. She initially kept the lines a secret. Later, in the episode, Lee Ji-wook discovers that the glasses show red lines and asks Shin Hyun-heup about it. She explains that the lines reveal a person's s*x life with their partners.

In S Line episode 4, after the motel case, Lee Ji-wook finds a pair of glasses and is shocked to see a huge number of red lines appear over his head, realizing Shin Hyun-heup was right all along.

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S Line eps 3-4 recap: Shin Hyun-heup becomes a witness to a crime at part-time work

In S Line episode 3, Shin Hyun-heup told Lee Ji-wook that his niece Kang Seon-a (Lee Eun-saem) would not commit suicide. Lee Ji-wook learned that Kang Seon-a was an outcast at school and that there was a girl who used to bully her. He learned that his bully, Kim Hye-young, had also been missing since that day.

Lee Ji-wook's superior at work wanted to close the case, labeling it a suicide; he confronted him, but nothing changed. Lee Ji-wook continued to work on this case privately. At school, teacher Jung-woo found the glasses and asked Lee Kyu-jin about them, and she encouraged him to wear them.

Jung-woo asked what she would do if she found out someone close to her was cheating on their partner. Lee Kyu-jin said she would watch it unfold like a morning drama. Notably, Jung-woo broke off his engagement after learning his partner had cheated on him with his friend.

Jung-woo reunited with his sister for the first time in years and met her child and husband for the first time. He noticed that his sister's husband, Kim Byung-chul, had multiple red lines over his head and appeared very suspicious of him.

Bang Sung-jin and Kim Hye-young’s photo outside the motel was leaked. The same day, it was reported that Bang Sung-jin had taken his life and left a suicide note. However, Lee Ji-wook believed that he didn't kill himself and thought someone was behind this incident.

As S Line episode 3 progressed, Jung-woo caught Kim Byung-chul with another woman at a hotel. He privately confronted Kim Byung-chul and told him to resolve his relationship within a day. The next day, Lee Kyu-jin asked Jung-woo whether the morning drama was over.

Jung-woo said he wasn't sure, but later, he saw the woman’s social media profile posting about gifts from Kim Byung-chul. He also learned that the woman was pregnant and rushed to his sister’s house. By the end of S Line episode 3, Jung-woo saw that his sister had crashed into Kim Byung-chul’s mistress’s car. Jung-woo asked if his sister was okay, but she stepped out of the car and revealed that he wasn't her husband, Kim Byung-chul, and his real name was Oh Tae-suk.

His mistress was actually his wife. After Jung-woo's warning, Oh Tae-suk ended things with his sister and was worried she might harm his real wife. It appears that Jung-woo left for Canada as planned. In episode 4 of S Line, Lee Ji-wook learned about Shin Hyun-heup's past and how she was a psychiatric patient. He was unsure whether to believe her, but her parents' story seemed more credible.

Shin Hyun-heup started working as a receptionist at a motel, and her friends are Oh Kyung-jin and Joon-sun. The three friends saw a staff teacher visiting the motel alone. The staff teacher also wore glasses and wanted to be an actress. She was heard practicing some lines in a motel room. She seemed interested in the music teacher and had a fantasy about having a red line with him.

Lee Ji-wook's colleague asked him if he was dating anyone, but he denied it. He said he was curious about someone, Les Kyu-jin, but didn’t want a physical relationship. Joon-sun took Shin Hyun-heup to a closed swimming area at school, where she became more comfortable with him and told him about the red lines she sees. Though she didn’t go into detail, Joon-sun believed her.

Later, the school staff teacher booked her usual room, which had a hole in the wall. One day, she peeped through the hole and saw the music teacher with a celebrity. The next day, she used a fire extinguisher to hit the celebrity woman before she could enter the motel room. The staff teacher, pretending to be the celebrity, entered inside, leaving the music teacher in shock. He tried to leave, but she threw a stapler that hit his head.

The music teacher passed out, and the staff teacher tried to get physical with him. She had spiked his water earlier and thought he had just fainted. However, soon the music teacher started bleeding from his head. The staff teacher again tried to get intimate with him. She later took her life in the bathtub.

By the end of S Line episode 4, the celebrity somehow escaped from the room she was locked in by the staff teacher. Shin Hyun-heup saw her and reported to the police.

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Viewers may catch up with S Line episodes 3 and 4 on Wavve.

Edited by Shreya Das