Best Mistake

Kim Yeon Doo is an ordinary high school student. But she has a stalker. To get rid of him, she uses a photo of some boy on the internet to pretend as if she has a boyfriend. But the next day, everyone in the school is staring at her, and Yeon Doo finds out that she's in trouble.

Yeon Doo thinks hard to escape disaster and comes up with an idea. She goes up to Hyun Ho and offers to be his delivery girl that brings bread to him every day whenever he wants. And Hyun Ho accepts her offer. After school, Yeon Doo goes to a bar to get her sister's wallet and spots Ju Ho at the bar with intimidating friends.

Ju Ho tells Yeon Doo that he saw her green backpack yesterday at a bar. And he tells her what he was doing there but also asks her not to tell anyone. After Yeon Doo promises not to tell anyone, they become closer. The next day, Hyun Ho helps Yeon Doo not to get penalty points. As Yeon Doo put bread on Hyun Ho's desk, she complains about Hyun Ho to Ju Ho.

After Ju Ho shared his secret with Yeon Doo, they become very close. Other students start to talk about them and Hyun Ho is bothered to see them being close. As Hyun Ho acts weird to Ju Ho, Ju Ho asks Hyun Ho what is the matter when he's not really dating him. Seol doesn't like her friends being involved with Yeon Doo.

Yeon Doo's stalker forces her to go home with him but luckily, her friend Yu Na repels him. They run into Hyun Ho and he offers to take Yeon Doo home. Hyun Ho asks her relationship with Ju Ho but she tells him that they're only classmates. At school, Seol couldn't stand seeing her friends taking care of Yeon Doo and not her. She finally explodes.

After what Yeon Doo heard from Seol, she can't stop thinking that she's fat. So she skips meals and eventually collapses. As she opens her eyes in the nurse's office, Ju Ho was sitting next to her. Ju Ho shows his drawings and tells a story about how Seol became who she is now.

Jin Soo digs up information about Yeon Doo. Hyun Ho asks Yeon Doo to have tteokbokki with him after school. While Yeon Doo waits for Hyun Ho, she finds Baekmoon High School students at the gate looking for her. Yeon Doo and Ju Ho manage to escape the crisis with the help of Yu Na. Yeon Doo forgets about Hyun Ho and as she heads to her house, she meets Jin Soo.

Yeon Doo keeps rejecting Jin Soo and tells him to go away, but Jin Soo won't go and threatens her. Luckily, Hyun Ho catches the scene and saves Yeon Doo. But Sae Chan ambushes Hyun Ho and Hyun Ho helplessly gets beat up. However, Sae Chan says he's done helping Jin Soo. And Yeon Doo decides to be Hyun Ho's right hand since he got hurt because of her.

Ju Ho leaves an umbrella in Yeon Doo's locker for her. But Seol takes away the umbrella and warns Yeon Doo to stay away. While Yeon Doo feels sad, Hyun Ho comes up to her and takes her home with his umbrella. Ju Ho recognizes his umbrella in the rain but it is Seol talking to Jin Soo who is holding the umbrella instead of Yeon Doo.

Dong Gu tells Ju Ho that it wasn't Seol who told Jin Soo about Yeon Doo's address. Ju Ho apologizes Seol and the two resolve their misunderstanding. Ju Ho asks Yeon Doo to watch a movie together, but she refuses. Instead, she makes a plan with Hyun Ho. Hyun Ho and Dong Gu become friends.

Yeon Doo and Hyun Ho go to watch a movie together. Yeon Doo appears dressed up, and Hyun Ho teases her. Before the movie starts, they play a game, and the one who loses must grant a wish of the winner. Find out who gets to win and what kind of strange wish the winner makes.

Hyun Ho studies hard and gets a perfect score on the vocabulary test. However, the teacher suspects him of having cheated in the test, and he gets upset and leaves the classroom. Ju Ho follows Hyun Ho and tells him to go back to the classroom and give an explanation, and they get into a fight.

The friends hold a birthday party for Yeon Doo. Ju Ho and Hyun Ho tell each other about their feelings for Yeon Doo. A subtle war of nerves happens between Ju Ho and Hyun Ho while Yeon Doo has no idea at all. Meanwhile, Ji sung writes someone's names on the paper.

Everyone is excited because of the festival. Hyun Ho, Ji Sung, and Ju Ho are all dressed up to scare people. Yeon Doo is the makeup artist for the day, but then some students come to Yeon Doo and say it's not fair that she's the only one who's not participating. And they lock Yeon Doo up on the third floor.

Hyun Ho finds out Yeon Doo who was trembling in the dark. And finally, Hyun Ho tells how he feels about her. Ju Ho sees them together and turns back with Seol. After Yeon Doo listens to Hyun Ho's sincere confession she decides to be together with Hyun Ho.