Jeon Dojun's new roommate is none other than Song Jaehee—his ex-boyfriend whom he ghosted back in high school. However, Jaehee claims the past is behind them, assuring Dojun that nothing will disturb their university life. Although Jaehee seems perfectly innocent, he secretly plots to win Dojun over once more.

When Dojun causes an accident that results in Jaehee breaking his arm, Jaehee asks Dojun to apologize by pretending to date him for a month until his arm is healed. Dojun is not too thrilled—but Jaehee takes this opportunity to seduce Dojun, discover what happened in the past, and maybe turn the four weeks of fake dating into a lifetime of true love.