Yun Wan, the disowned daughter of the Yun family, was sent to a Taoist temple as a child. They called it cultivation, but it was really exile. Ten years later, hoping to curry favor with the foremost immortal sect, the Tianyan Sect, her family decides to marry their legitimate daughter to Li Yuan, the sect's legendary young master, whose cultivation has been crippled and whose life is said to be nearly over. When the legitimate daughter refuses, the family forcibly summons Yun Wan home and makes her take her place.
On her wedding night, everyone expects Yun Wan to become a widow and the butt of their jokes. But inside the dying Li Yuan, she senses the aura of a pure and powerful ancient sword bone. It is the perfect “sword sheath” and “furnace” for the Heartless Sword Dao she has painstakingly cultivated for ten years. She doesn't flee. Instead, she takes the initiative, using her sword intent as a guide. Not only does she save Li Yuan's life, she also uses the sword bone within him to break through the final barrier in her own cultivation.
From then on, what everyone saw as a farce of a marriage between a good-for-nothing and a cripple becomes a formidable alliance of equals. Yun Wan is no longer a disowned daughter the family can push around. With a three-foot blade in hand, she delivers face-slapping justice to the elders who look down on her, exposes her half-sister's hypocritical facade, and claims her place within the Tianyan Sect. When her family tries to use her again, she severs every family tie with a single stroke and declares, “My life has never belonged to the Yun family.”
She and Li Yuan begin as “contract spouses” using each other for their own ends. But as they fight side by side, face the sect's internal power struggles, and fend off invasions by demons from beyond its borders, real feelings gradually bloom between them. In the end, Yun Wan uses her supreme swordsmanship to help Li Yuan restore his meridians and ascend to the pinnacle of the immortal path. She, too, becomes an undying legend whose sword can change the very color of heaven and earth.
