Beomgyu has a twin sister, Nayeon — they look almost identical, except he’s a boy and she’s a girl. When Nayeon breaks her leg and can’t attend her elite private academy, she begs Beomgyu to take her place for one semester. He refuses at first, but she threatens to tell their mom about his skipped classes, leaving him no choice.

Now Beomgyu has to wear a girl’s school uniform, a wig, and pretend to be Nayeon every day. Slowly, he starts getting used to his new identity, trying his best not to raise any suspicion. But living as his sister turns out to be far more complicated than he ever imagined.

Things get even messier when Beomgyu meets Choi Yeonjun — the guy who’s been head over heels for the real Nayeon.