Duke's daughter Shannon regains the memories of her past life the moment she meets her new stepbrother, Silvan, after her mother's remarriage. She realizes the world she is in matches the novel The Black Knight and the Praying Princess, and that she is the minor stepsister Shannon Tia Freulein, whose only role is to be mercilessly killed by the story's handsome, cruel hero, Silvasta. Terrified of the young Silvan, who already acts like a tyrant, Shannon tries desperately to flee and avoid her fated death. But a chance incident reveals his true, vulnerable nature beneath the cold exterior, and she begins to see him not as a monster but as a lonely boy in need of care. As she grows closer to him, his obsessive affection for her intensifies, and he declares that everything about her belongs to him.

Years later, with Silvan now grown, the original plot begins to unfold. Shannon, still working to secure a happy ending, tries to push Silvan toward the novel's heroine, Mia. Yet Silvan shows no interest in Mia and instead turns his possessive love fully on Shannon. Despite her own growing feelings, Shannon struggles with the fear that she might still be killed or that her presence will lead Sylvain down a dark path. When a poisoning incident throws the royal court into chaos and leaves Shannon unconscious, Sylvain, following the original story, suspects the prince and considers a terrible choice. Shannon must uncover the true conspirators and find a way to prevent Sylvain from becoming the story's tyrant. In the end, Sylvain confesses his love openly, and Shannon accepts, breaking the novel's tragic course and forging a new future together.