Plot synopsis

Like his swimming champion father, Won-il (Seo In-guk) was once a promising swimmer. But when his father dies during a swimming competition (where he was doing his specialty called "no breathing"), followed soon after by his mother's death, Won-il quits swimming for good. Instead, he lives life hopelessly and recklessly, like there is no tomorrow. With Won-il in danger of being expelled from school, his father's longtime friend Jae-suk (Park Chul-min) drags him to a physical education-focused high school, hoping that he'll start swimming again. There he meets his long-ago rival, Woo-sang (Lee Jong-suk) who in the past had always been overshadowed by Won-il. With Won-il's absence from the sport, Woo-sang is now in first place and is a national swimming star. But he gets disqualified from the national tryouts after getting into trouble, so he has to start from ground zero and ends up at the same phys-ed school as Won-il. Woo-sang is Won-il's complete opposite in personality, and all he cares about is winning so he finds Won-il's return to the sport unwelcome. Then there is Jae-suk's daughter, Jung-eun (Kwon Yuri) who captures both Won-il and Woo-sang's hearts and further reignites the rivalry between them. The two very different young men begin training for an upcoming swimming competition, battling for love and friendship as they undergo the rite of passage of growing up.