A top secret agent travels through time overnight, reduced to Ye Xiyun, a trash young lady of the Ye family whom everyone can bully. Crucially framed and poisoned with a deadly venom, in a desperate situation she accidentally breaks into the cold pond and encounters Jiuye, the Emperor of the Everlasting Night Demons. He is cold and ruthless, with an ingrained possessiveness. For ten thousand years no one has been able to break free from his heart-confusing art, except her. To cure the deadly poison on her body, Jiuye painfully offers a drop of precious heart's blood to help her break through her meridian seal, and brands her collarbone with an exclusive heart-locking mark. From then on, an entangled destiny slowly unfolds. Human conflicts and demon conspiracies follow one after another, and that love planted with heart's blood will ultimately stir up monstrous waves between the immortal and demon realms.