20-year-old Kyeong-soo is a man who's full of assumptions. He learned about sex from Internet porn, but nothing about the real thing. He's only had crushes and has never even kissed before. He got embarrassed when he confessed his feelings to Ji-yeon, his crush. He comforted himself from the shame with Japanese girls in his room with his right hand. One day, he has a fight with his father and remembers his friend Baek-hyeon had invited him over to Gangwon-do. There he falls in love with his friends' mother.

Jay, an international student from Thailand, comes to Korea to see his friend Seong Hun. The two enrolled in the same college class called "Health and Happiness" and need to submit a physical body assessment for their final project. While Seong Hun already works out regularly, Jay isn't in the greatest shape and struggles in the gym. Enter Jin Uk, a personal trainer who takes a special interest in Jay, much to Seong Hun’s displeasure. However, there's something strange about Jin Uk. Despite his kindness toward Jay, suspicions begin to rise that Jin Uk may be involved in a murder and missing person incident. Is there a happy ending in store for Jay and Seong Hun, or will Jay's budding relationship with Jin Uk cost him an unspeakable price?