“We are neither kids nor adults. When do we become adults then?” Min Jae and Seo Yeon are no different from ordinary 17-year-old high school students. Min Jae is silent and sensitive, yet a good student. Seo Yeon who plays the piano wished to enter an arts high school but failed. As they grow into adults, their surroundings and the reality they face get harsher. These two somehow similar but different friends get closer as they overcome their growing pains together.
Cellphone app Joalarm is created. If someone likes you and they are within 10 meters of you, the alarm for the app rings. The app also shows how many people like you, but the app doesn't reveal specific details on who likes you.
Kim Jo-Jo (Kim So-Hyun) is a high school student. She is pretty and smart. She seems like cheerful person, but her parents died when she was young. Since the death of her parents, Kim Jo-Jo has lived with aunt's family. Living there is not easy for Kim Jo-Jo. She doesn't download the app Joalarm.
Meanwhile, Hwang Sun-O is a popular male student at the same high school where Kim Jo-Jo attends. He is the son of a wealthy family, but he is not loved by his parents. His best friend Lee Hye-Young also attends the same high school. Hwang Sun-O notices that his best friend Lee Hye-Young likes Kim Jo-Jo. Hwang Sun-O wants to know if his friend really likes her, so he kisses her.
Mo Seok-hee is an only child and her father runs the large company MC Group. She is beautiful, smart and rich. Mo Seok-hee appears like she is arrogant, but she struggles over her mother’s death. Her mother was killed 15 years ago. Meanwhile, Heo Yoon-do is a lawyer, but he doesn’t even have an office. He solves small problems of neighborhood residents at a restaurant. He is full of love. Miraculously, Heo Yoon-do is headhunted to join the TOP team at MC Group. The TOP team manages the affairs of the family who runs the MC Group. Their job includes covering up immoral or illegal behaviors done by the family.
Jenny Jang (Kim Sun-A) is poor and works at bathhouse in Gangnam, Seoul. She starts a new job as a housemaid for a conglomerate family. She becomes successful and then runs J Boutique. She also begins work as a lobbyist. Jenny Jang gets involved in an international city development project.
A romantic comedy which is about a timpanist witnessing a murder case but cannot remember anything about what happened. With the help from a mysterious guy, she attempts to recover her memories from that day.
Ki Moo-Hyeok, a lawyer with a high winning rate, only cares about money. Due to a murder case at a high school which he deals with, his reputation as a lawyer hits rock bottom. To regain his good name as a lawyer, he sneaks into the high school and work as a temporary teacher. He tries to reveal a secret which the students have, and gets involved with Teacher Ha So-Hyun, a P.E. teacher who loves her students. They then face the students'secret.
Yoon Jong-Woo is a man in his 20's. He has lived in a small town for all of his life, but he gets a job at a small office in Seoul. Yoon Jong-Woo moves out to Seoul and stays at a cheap apartment which shares its kitchen and bathroom with other residents. He doesn't like staying at the apartment and he doesn't like the other residents who seem weird and suspicious.