A story of love and friendship between five high school students from Seoyeon High School. Lee Ha-Min (Seo Ji-Hoon) appears like a bright person, but there is also darkness within his mind. Han So-Mang ( So Ju-Yeon) is a warm-hearted person, but she is also quite timid. Lee Jae-Min (Kim Min-Kyu) is a popular student with a painful past. He is kind to everyone around him. Yoon Bo-Mi (Kang Hye-Won) is a sweet, model student. Choi Jin-Young (Yoon Hyun-Soo) loves playing games. He can seem unfriendly and has a delicate personality.

Soo-hyun, who has recently moved into a new house, buys a used washing machine through a second-hand app but finds out it doesn’t work. Annoyed by the seller’s irresponsibility, she leaves a comment calling the seller a con man, and reports it to the police. Little does she know that the seller is a psychopathic serial killer who uses an online second-hand market to lure his victims. Her comment renders his hunt for a new victim all but impossible so she becomes his next target. She starts receiving obscene phone calls, countless unwanted food deliveries, and strange men knocking on her door looking for a good time. A trip to the sender’s address proves deadly serious when the police and Soo-hyun find a man’s dead body.