S Line: When will episodes 3 & 4 air and what to expect?

S Line dropped the first two episodes starring Lee Da-hee, Lee Soo-hyuk, Oh My Girl’s Arin, and Lee Eun-saem on Friday, July 11, 2025. S Line tells the story of a girl, Shin Hyun-heup (Arin), who has been able to see red lines appearing on people's heads since she was a child. These red lines indicate the number of people they have had intimate relationships with.

Shin Hyun-heup's life takes a turn as a pair of glasses emerges, allowing others to see these red lines and revealing secrets about their intimate life. As people wear these glasses, their desire to know more about others increases, creating a ruckus around them.

Lee Soo-hyuk portrays the role of a detective named Han Ji-wook who does not quest to know the truth about the S Line, while Lee Da-hee plays a high school teacher called Lee Kyu-jin. Actress Lee Eun-saem depicts the character of Kang Seon-ah, Han Ji-wook's niece, who soon finds the glasses that show the S Line.

S Line episodes 3 and 4 are scheduled to be released on Friday, July 18, at 11 pm KST on Wavve. Viewers may expect Han Ji-wook to find more clues about the man who tried to kill women, after seeing a wall full of red lines at his place. Meanwhile, Shin Hyun-heup witnesses Kang Seon-ah falling from the school rooftop, leaving viewers wondering whether Kang Seon-ah survives.

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S Line episode 1 and 2 recap: Shin Hyun-heup goes back to high school due to the red lines

In episode 1 of S Line, it is shown that Shin Hyun-heup, who has been able to see red lines since she was born, faces a hard time after her mother kills her father and disappears. Her mother found out that her father was cheating on her through a sketch made by Hyun-heup showing multiple red lines connecting with other women.

Shin Hyun-heup locks herself up and has suicidal thoughts. Despite her attempts at taking her own life, she somehow survives or heals on her own. Later in episode 1 of S Line, Han Ji-wook investigates a case where a deliveryman killed a girl.

Shin Hyun-heup called the cops as she saw a person with a similar helmet and outfit enter the house of a lady living across from her place. When Ji-wook arrives at her place, she tells him they were just a couple and that she was mistaken.

As the first episode progresses, Shin Hyun-heup tries to save that lady again from the suspected deliveryman, who tries to kill her. The man has one red line, which, according to Shin Hyun-heup, was rare. He had a motive to take down people who had sexual relationships with multiple people.

Lee Ji-wook arrives in time and shoots the man, saving both the lady and Hyun-heup. The attacker named Jeong-min had violent charges registered against him in the past. Lee Ji-wook was unaware of the man's motives but only got curious since there was no logical reason they could find for his killings.

Meanwhile, Kang Seon-ah, with one red line, is an outcast at school and bullied by her peers. She lives with Han Ji-wook but does not like him, as she was once seen saying he would abandon her again. It was revealed that Shin Hyun-heup and Kang Seon-ah were in the same batch in middle school.

Stills from S Line (Images via Instagram/@wavve.official)

By the end of episode 1 of S Line, Shin Hyun-heup receives an anonymous message saying that they also see the red lines, asking her to rejoin the high school.

In episode 2 of S Line, Kang Seon-ah finds a pair of glasses in her locker, and when she wears them, she starts to see red lines. Kang Seon-ah soon figures out it's related to relationships when she sees her bully, Hye-young, having a red line connected to a teacher.

She is shocked to see Ji-wook with a huge number of lines and learns that Lee Kyu-jin has no lines. Notably, Lee Kyu-jin, her homeroom teacher, stops the bullies from attacking Kang Seon-ah and also looks out for her at school.

Han Ji-wook’s increasing curiosity about Jeong-min leads him to search for the glasses he wore, which were missing from the evidence box. Jeong-min was a mathematics teacher at Kang Seon-ah’s school. He meets Lee Kyu-jin to learn more about Jeong-min, and she informs him about Seon-ah’s situation at school. Lee Kyu-jin says that she never saw Jeong-min wear any glasses.

Meanwhile, Kang Seon-ah threatens Kim Hye-young about her relationship with teacher Bae Sung-jin, sending her a photo of them entering a motel. Since she is a minor, Kim Hye-young called Kang Seon-ah a fool for using it against her. However, she gets curious about how Kang Seon-ah found out about them.

Later, in their school's washroom, Shin Hyun-heup tells Kang Seon-ah that she can see the red lines and warns her not to meddle in people's lives. Kim Hye-young overhears them and later steals the glasses.

Kang Seon-ah, wanting to move out of her house, threatened Bae Sung-jin to give her money. By the end of the S Line episode 2, she meets Bae Sung-jin at the school rooftop, where he pleads with her not to release the photos since he has a family and is expecting a second child with his wife.

Kang Seon-ah does not back down and confronts him for not stopping the bullies even when he knew about it. Bae Sung-jin receives a message from his wife, including the photo taken by Kang Seon-ah. He becomes furious, believing Seon-ah sent the pictures.

Stills from S Line (Images via Instagram/@wavve.official)

Notably, Kang Seon-ah had asked Shin Hyun-heup to come to school, as she was meeting Bae Sung-jin. As Hyun-heup arrives, she sees Seon-ah falling from the top. When a person dies, the red line disappears, but it is not shown whether Kang Seon-ah’s red line disappears.

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S Line episode 3 preview

As per the preview, after Kang Seon-ah’s fall, Shin Hyun-heup appears to be looking for evidence against Bae Sung-jin. She meets a girl at the rooftop named Lee Kyung-jin from Class 5, who seems to be interested in Kang Seon-ah’s case. Meanwhile, Han Ji-wook asks Lee Kyu-jin whether she thinks it was a “suicide” case, hinting at the possible death of Kang Seon-ah.

Additionally, another teacher found the glasses, unaware that they had been used by Kang Seon-ah before. Lee Kyu-jin suggests that the teacher wear the glasses, and soon it is shown that he breaks up with his girlfriend, with whom he was planning to marry.

It seems that the teacher found out his girlfriend was cheating on him with his friend. The teacher asks Lee Kyu-jin what she would do in such a situation, and she replies that she would see it through till the end and watch them fall apart.

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Meanwhile, viewers may catch up with the first two episodes of S Line on Wavve.

Edited by Ameen Fatima