Modern forensic expert Yan Weichi dies in a medical dispute—only to awaken as a concubine-born daughter forced to marry in place of her legitimate sister in the Great Li Dynasty's Pingyi Marquisate. Trapped in a dungeon, she saves the deposed Crown Prince Shangguan Xi—poisoned with a rare toxin and framed by enemies. Using cutting-edge forensic science and medical expertise, she clears his name, restores him to the throne as heir apparent—and becomes the undisputed Crown Princess.