In the opening of Episode 1 of "Idol I," we are introduced to Maeng Se-na, a young defense attorney whose mind is filled with dreams. She imagines being face-to-face with her favorite person in the world and yearns to make them happy. Despite her busy schedule during the day as a law student, Se-na dedicates her nights to being a devoted K-pop idol fan, particularly of Golden Boys' lead vocalist, Da Ra-ik.
That day, Se-na defends tennis player Lee Seong-ho in a case of blackmail and assault, despite strong public opinion against him. She successfully proves Seong-ho's innocence, and he is acquitted. Addressing the media on his behalf, she threatens legal action against anyone who continues to defame him. News reports suggest that the prosecution will seek a retrial, but Se-na's colleagues call for a celebration. They wait at the law firm for her return, discussing how her actions have prompted an emergency meeting at the district office and how she is being named a partner at their firm despite her young age.
Se-na returns after the hearing and prepares to clock out. Both senior and junior lawyers urge her to stay and celebrate her victory and promotion, but she declines, saying she has an important engagement that evening. The lawyers remark that Se-na has no friends or romantic relationships and wonder what could be occupying her time.
In reality, Se-na is heading home early because Ra-ik has released a new solo single. She listens to it while driving and, once home, changes into her pyjamas and streams the song. Her room is filled with posters, standees, and merchandise of him. She is pulled out of her trance when her friend Chun-jae shows up with fried chicken and beer. Though she initially ignores him, she eventually invites him in. Chun-jae jokes that she looks like an obsessed fan, but Se-na dismisses the remark, explaining that her love for Ra-ik as a fan is different from romantic love.
The following day, Ra-ik is escorted to the stage for his solo debut performance, only to be confronted by an obsessed fan who lunges at him before security can intervene. In the dressing room, Ra-ik laments the absence of proper stylists, makeup artists, and costume designers. His manager kneels before him, pleading for cooperation. After a heated exchange, Ra-ik reluctantly agrees. As he performs, Se-na struggles to sit through a court hearing, faking a respiratory illness as the prosecution drones on. She urges the judge to make an immediate decision when he considers granting them more time.
Se-na steps out to the restroom and collides with lawyer Kwak Byeong-kyun, spilling coffee on his shoes. Upset by her lack of apology, he waits outside the restroom, unaware that Se-na has already slipped out in her sweats. She later seeks Chun-jae's help in exposing a concert ticket scalper.
Meanwhile, Ra-ik heads to a fan meeting, receiving nonstop calls and messages from unknown numbers. Realizing his number has been leaked, he panics. At the fan meeting, the obsessed fan shows up and causes a scene, accusing him of repeatedly changing his phone number. Overwhelmed, Ra-ik suffers a panic attack and hides in the restroom with his anti-anxiety medication. Se-na arrives at the venue only to see fans leaving and feels defeated. She worries that her job keeps her from meeting her idol but promises to continue loving him from afar.
That night, Ra-ik looks through old photos of his ex, whom he spotted at the fan meeting. Drinking alone, he reflects on how his life revolves entirely around his career. Suddenly, two obsessed fans break into his apartment.
Ra-ik, intoxicated, lashes out at the girls, and they secretly film the confrontation and upload it online, sparking a major controversy. His manager and agency CEO scold him for worsening the situation. Ra-ik calls the CEO greedy, pointing out how the agency profits endlessly from his work. He learns that his solo song has dropped to tenth place on the charts on its debut day due to the scandal.
When Ra-ik insists he is the victim, the CEO argues that idols must maintain a flawless image and that he lost his humanity the day he chose this career. Meanwhile, Se-na tries to buy tickets for Ra-ik's upcoming concert but finds them sold out instantly. She contacts a scalper and agrees to meet outside the venue.
On the day of the concert, Ra-ik struggles with anxiety and visits a therapist, arriving late and angering his manager. The Golden Boys members wait for him as fans begin to gather. Once Ra-ik arrives, the crowd recognize him, forcing staff to rush him inside.
Outside, Se-na confronts the scalper and threatens legal action. The man flees without taking her money or returning the tickets, prompting Se-na and Chun-jae to chase him. Se-na mistakenly follows Ra-ik, thinking he is the scalper. She pulls down his mask and freezes when she realizes who he is. Ra-ik pulls her close to hide from pursuing fans while Se-na stares at him in disbelief.
Inside the venue, Ra-ik's bandmates scold him for his lateness. Jae-hee insults his talent, and their argument escalates into a physical fight. Young-bin steps in to mediate but is shoved, fracturing his arm. He is rushed to the hospital with Jae-hee accompanying him, while Ra-ik is forced to stay behind and perform the solo concert.
At home, Se-na watches the concert online, replaying her brief encounter with Ra-ik. She later learns about Young-bin's injury and spirals into online comments accusing Ra-ik of mistreating Jae-hee. Despite the backlash, Se-na continues defending him online.
After the concert, Ra-ik drinks with Woo-seong, the only remaining Golden Boys member. They discuss his fight, his career, and his personal goals as an idol. The next morning, Ra-ik awakens to find Woo-seong dead in his living room, lying in a pool of blood. The episode ends with Se-na watching news reports of Ra-ik's arrest for his bandmate's murder as she rushes to the police station and volunteers to represent him.
