Story follows four young men who have just turned 21 years of age.　　Lee Choo-Won (Seo Jun-Young) is an athlete who can not forget his past love. Ma Goo-Rim (Baek Sung-Hyun) was once a popular singer, but because of a drug scandal is mired in despair. Choi Seo-Won (Choi Tae-Hwan) is a medical student at prestigious Seoul National University, but he has leukemia. Sung Dae-Sung (By..时空访客