In a prep-class for year-end exams, a sadistic killer puts the students through mind-games in order to save each other.
Along with his young son, Ji-ho, Woo-jin misses his wife Soo-a, who died after promising to return a year later with the rainy season. Miraculously, they reunite with Soo-a when the rainy season comes around, but she has no memory of her husband and son whom she dearly loved.
When the crown prince is killed, his twin sister assumes the throne while trying to keep her identity and affection for her first love a royal secret.
