To prevent extremists from instigating war with neighboring Ostania, Twilight, Westalis's top agent, must investigate Ostanian politician Donovan Desmond by infiltrating his son's prestigious school, Eden Academy. Under the guise of Loid Forger, a doctor, Twilight adopts the orphan Anya and enters into a fake marriage with Yor Briar, enrolling Anya in Eden Academy without knowing that both of them share secret identities: Yor is an assassin known as "Princess Thorn," and Anya is a psychic with the ability to read minds. Although initially a fake family where all three exploit each other, over time they gradually realize the importance of the other two in their hearts.