*Under the treadmill, there is still sperm left. A popular fitness club in Seongwang-gu, Yonggeun Fitness Club offers something so interesting and different from other fitness clubs. In particular, the night class is a very popular class with male members rushing to register. The building owner 'Sun Bin' finds a strange thick liquid after the night class and decides to investigate what really happened in the night class. It turns out that the night class is a place where something unpredictable is under the guise of a fitness class?! "How dare you do this in my building. I will kill you!*''