Crash Course in Romance

Choi Chi Yeol is a famous mathematics teacher at a prestigious The Pride academy. He doesn't have time nor interest in women or anything else beside his work. He has trouble sleeping and barely eats, and when he does eat he often throws up. One day, his assistant brings him a bento lunch from a place where Nam Haeng Seon works. Choi Chi Yeol reluctant at first, and without an appetite, he decides to try and eat. To his surprise, he finds is delicious and nostalgic, and it sits well with his stomach. What he doesn't know, is that owner of that place is Nam Haeng Seon who chased him not too long ago when he stole her brother's phone thinking he was trying to get a gossip photo of him.

Choi Chi Yeol visits the place where Nam Haeng Seon works, but disguises himself not to be recognised while buying food. Nam Haeng Seon is trying to get her daughter into The Pride academy where he works. Her daughter isn't her real daughter, and she is in fact her aunt. Some ten years ago, her older sister simply left her daughter at the doorstep and asked Nam Haeng Seon to look after her, which she did, despite having to give up her position as a national volleyball professional.

After being shot at with a mysterious assailant using metal balls and a slingshot, Choi Chi Yeol and Nam Haeng Seon go to police to report the crime. He thinks he may have been the target because of his celebrity status, but the constable there has never even heard of him. Eventually, Nam Haeng Seon find out that Choi Chi Yeol is the actual star teacher that her daughter talks about all the time and starts going overboard to appease to him, though he retains his cold demeanor and focuses on teaching.

Nam Haeng Seon is trying to get her daughter enter a special 7-student class, for which her daughter qualifies, but one of the mom's makes things complicated which get Haeng-Seon's daughter replaced with another student. Chi-Yeol goes to the principal in protest, but is pushed against the corner and his protest fails. In secret, he offers to teach Chi-Yeol's daughter in his spare time in return for Chi-Yeol's free meals.

Chi-yeol and Haeng-seon discuss the terms of tutoring to both sides' agreement. The most important thing is to keep it a secret because that could bring unnecessary problems. One night, Haeng-seon is drinking and Chi-yeol is trying to make her stop but she tells him she will not go until she finishes the bottle. He helps her to speed things up, but his alcohol tolerance is very low and she ends up towing him to her place. In the morning, he storms out as fast as he can, but forgets his belt. As she brings it outside to give it to him, they are spotted by her best friend and his assistant who were wondering why his car is parked so early in the vicinity.

Neither Chi-yeol's assistant nor Haeng-seon's best friend are happy about not being in the loop of the whole deal about tutoring Haeng-seon's daughter. Chi-yeol goes off radar for a while, and in a strange coincidence, Haeng-seon and her family runs into him when going camping. One of the moms becomes suspicious and finds out that Chi-yeol is visiting Haeng-seon's place after hours.

Chi-yeol manages to deceive one of the moms tailing him to make it appear as if he came to buy food, but the shop was closed. Later they play match, men versus women, and lose bigtime and Chi-yeol injures his wrist. Slowly, he is starting to get attracted to Nam Haeng-seon and confides to his psychiatrist about it. To try and shake it off, he goes on a date with young and beautiful renowned pianist who has a crush on him.

Chi-yeol and Haeng-seon are having dinner at her mom's old restaurant. Little does she know that Chi-yeol considers her mother as his saviour when he was young and studied but didn't have money, she fed him almost for free every day. Chi-yeol starts thinking that this is the connection that seems to attract him toward Haeng-seon, the appreciation rather than love. So he secretly buys their place and cuts the rent in half. Also, pays for installment of all air conditions in the building. Finally, Chi-yeol realises his feelings for Haeng-seon are real when he ditches his date at piano recital and goes straight to her. But, the jealous moms were waiting and catch them in the act.

Choi Chi-yeol tries to explains all the moms about his private tutoring, but is eventually forced to suspend it. He does provide Nam Haeng-seon's daughter with learning materials and has confidence she can do it on her own. She still has problems in school since gossips surrounding her tutoring lessons. But she has good friends at school that take to her defense. Choi Chi-yeol ends up clearing up the confusion regarding Nam Haeng-seon on TV, confessing that he fell in love, and not the other way around.

Nam Haeng-seon is struggling with Choi Chi-yeol's public confession as she still appears as married to the public. However, her daughter tells the truth in front of the camera that Haeng-seon is in fact her aunt who raised her, and that she is single.

Now that it is clear that Nam Haeng-seon is single, Choi Chi-yeol does not waste time about coming for her. They star dating, his staff returns to work for him, and other moms apologize to her for the misunderstanding. At the same time, the police are closing in on their prime suspect for murders using metal balls.

As Chi-yeol's and Haeng-seon's relationship progresses, Chi-yeol's assistant is starting to show his true self. The police have caught their prime suspect, and it turns out he isn't the killer but the key witness to a murder.

Things are getting worse and Chi-yeol's assistant is clearly trying to harm or eliminate Nam Haeng-seon. While Haeng-seon is unaware of just how serious this all is, her daughter gets kidnapped and then involved in a traffic accident.

Nam Haeng-seon's daughter is hospitalized and underwent surgery successfully, but is in coma. Unexpectedly, her real mother appears though it is obvious her interest is only in getting some of Chi-yeol's money. Chi-yeol is setting a trap for his assistant and pretending like everything's normal so he can follow him and find out where he lives.

Chi-yeol finds out where his assistant lives and discovers everything upon entering his apartment. His assistant feels trapped when he overhears that Haeng-seon's daughter is showing signs of getting better and decides his only way out is to kill her. He is stopped in the act and Chi-yeol chases him up to the roof where he confesses everything before jumping to his death. Haeng-seon's daughter regains consciousness and is undergoing rehabilitation. Her best friend finally gains courage to tells her he's in love with her, but she does not give him definitive answer for now.

Nam Haeng-seon's daughter tells everyone she's going to live in Japan with her biological mother so her mother stops asking Chi-yeol for money. Eventually, her real mother sees that her daughter does not want to go but is sacrificing herself for her aunt, and leaves alone. Gossips start spreading after Chi-yeol had a coffee with his old date, and due to circumstances, both Chi-yeol and Haeng-seon propose each other at the same time. Haeng-seon's daughter also gives her answer to her best friend, that she too is interested in him, and they become a couple.