In the fourth episode of The WONDERfools, we're treated to a flashback where Dr. Ha first encounters Ju-ran, a young girl with a hearing disability. Dr. Ha, a compassionate scientist, gifts her with hearing aids, which she cherishes. The scene then cuts to the devastating fire at Hawondo Lab, where Dr. Ha instructs Pal-ho, Ju-ran, and Ho-ran to hide until he's released from prison.
Years later, Dr. Ha emerges from prison and rekindles the Wunderkinder project, commanding the trio to search for the elusive Child of Eternity.
The episode shifts to the present day, where Dr. Ha, Ju-ran, and Ho-ran meet Jeon-bok, also known as Madame King. Dr. Ha holds Jeon-bok responsible for the past and accuses her of funding the experiments. Jeon-bok counters that she only supported the project because she believed it would help the children. Dr. Ha presses her for information about the Child of Eternity, and Ju-ran uses her powers to extract information from Jeon-bok. However, Jeon-bok insists that the child is long dead. Dr. Ha recalls that the Child of Eternity could never die, despite the numerous experiments conducted on him.
A flashback reveals Un-jeong witnessing the painful experiments being conducted on the young boy. Unable to bear it any longer, Un-jeong uses his powers to stop the experiment, ultimately triggering the fire that destroys the lab.
Back in the present day, Un-jeong awakes from a nightmare about the incident. While asleep, he unknowingly activates his powers, causing damage both inside and outside his house. Meanwhile, Jeon-bok realizes that Dr. Ha manipulated information about the Child of Eternity during their conversation.
Coincidentally, Dr. Ha and the trio are leaving when Ho-ran spots Chae-ni outside trying to use her powers to visit the Northern Lights—something she's always dreamed of. The next day, Chae-ni brings Gyeon-un and Robin to City Hall to join her for a street cleanup drive. The trio asks Un-jeong to train them to control their powers, but he appears frustrated and distant. Just then, members of the Church of Salvation arrive at City Hall, which immediately angers Un-jeong. He takes Chae-ni, Ro-bin, and Gyeon-un away from the area and tells them to learn how to control their powers on their own. He instructs them to repeatedly trigger their abilities until they can use them properly to their advantage.
Elsewhere, Dr. Ha learns that the experiment involving Bong-pal has failed and orders the scientists to kill him. Yu-ran begins to worry that Dr. Ha will kill them too if the side effects of the experiments are never cured. However, Ju-ran tells her to continue trusting Dr. Ha and orders her to keep searching for the Child of Eternity.
Meanwhile, Jun-mo meets Jeon-bok and shows her CCTV footage of Dr. Ha and the trio leaving a restaurant the previous night. In the footage, Chae-ni is testing her powers when Dr. Ha orders Pal-ho to kill her. Just as Pal-ho is about to attack, Chae-ni suddenly teleports away—leaving everyone stunned and questioning what's truly at stake in this mysterious quest for the Child of Eternity.
In another part of the story, Jeon-bok attempts to reach out to Chae-ni but mistakenly connects with Jun-mo's phone. Realizing the person in front of her is not Jun-mo, she soon deduces that it's Ho-ran using her hallucination powers to gather intel on Chae-ni.
Ho-ran accuses Jeon-bok of abandoning her and once again questions her about the Child of Eternity. She employs her hallucination powers to intimidate Jeon-bok but fails to penetrate her resistance. Jeon-bok then urgently requests Jun-mo to locate Chae-ni as swiftly as possible.
In parallel, Gyeon-un, Ro-bin, and Chae-ni discuss their aspirations with their powers. Chae-ni expresses a desire to witness the Northern Lights, while Gyeon-un confesses his wish to make his daughter proud of him. Ro-bin reveals his intention to show off his powers to the high school bullies who once tormented him.
As they continue experimenting with their abilities, they gradually uncover how their powers operate. Chae-ni realizes that she teleports whenever her heart rate surges. Ro-bin concludes that his powers activate when he experiences intense emotions, while Gyeon-un discovers that he sticks to objects when he lies or becomes nervous.
Meanwhile, Pal-ho arrives at the junkyard where Un-jeong is leading a cleanup effort. Un-jeong promptly uses his powers to halt him, but Chae-ni inadvertently teleports to the scene. She swiftly teleports back to the room and brings Ro-bin along to assist Un-jeong.
At the junkyard, Chae-ni tries using her powers to teleport Un-jeong and Ro-bin away, but she struggles to control her ability on command. Un-jeong explains that Pal-ho is a Wunderkinder, accounting for his superior power compared to theirs. Ro-bin and Un-jeong unite their abilities to combat Pal-ho.
However, Chae-ni notices that Un-jeong is growing weaker during the fight. She hugs him and, by accident, teleports him away from the junkyard, leaving them both beneath the Northern Lights. Meanwhile, Ro-bin is overcome by emotion and manages to block Pal-ho's attack by stopping the car that was thrown their way.
Chae-ni and Un-jeong suddenly arrive beneath the Northern Lights, where Chae-ni slowly bleeds to death. Back at the junkyard, Pal-ho attempts to kill Ro-bin but fails. Elsewhere, Jun-mo searches for Chae-ni and discovers Gyeon-un stuck to the ceiling inside a room. He questions Gyeon-un about Chae-ni's whereabouts.
At the same time, Un-jeong desperately tries to resurrect Chae-ni. Moments later, Chae-ni suddenly wakes up as the episode comes to an end.
This story depicts a dramatic scene where Chae-ni and Un-jeong are transported to a beautiful but eerie place beneath the Northern Lights while Chae-ni struggles with her injuries. Meanwhile, Ro-bin's bravery in defending himself against Pal-ho's attack adds tension to the plot. Jun-mo's search for Chae-ni and Gyeon-un's discovery add further intrigue to the story. Finally, Un-jeong's desperate attempt to save Chae-ni creates a cliffhanger as she suddenly wakes up at the end of the episode.
