The day before his high school graduation, Ki Ha-neul is in a car accident. Ten years later, he wakes up in an unfamiliar hospital, disoriented and confused. As if that isn't enough, he finds himself in the arms of a devastatingly handsome man whose mere presence makes his heart pound. "Who are you?" Ha-neul asks, breathless. "Your lover. Your boyfriend." The man is Yeo Sae-byeok, the very person Ha-neul cut ties with after losing his first girlfriend. Now, at twenty-nine, Ha-neul is told they've been dating for seven years and living together for nearly four. It's absurd. Impossible. Ha-neul refuses to accept this reality and pushes Sae-byeok away, but circumstances force him to reluctantly move in with the man. As days pass, Ha-neul finds himself asking a dangerous question: why does his heart race every time he looks at this stranger who claims to be his enemy?