Seo Hae-young, the only light of Yoon Hae-won, who has no money, no family, and no future. After her friend Ko Tae-gyeom reveals her feelings for him, Hae-won's life begins to fall apart. Tae-gyeom demands a relationship through threats, Hae-young wields violence in an unknown manner, and another friend, Joo Hyun-woo, joins... The relationship between the four of them is broken, memories of the past that are now faded. Who will win the irreversible game?