"The Shadowless Sword" describes the love entanglement and fate of men and women in troubled times. It is a martial arts film that describes the stories of three heroes in the Bohai era. Lee Seo-jin plays the second prince Daejeong-hyeon, who is exiled because of political struggles when his country is facing extinction. He is ready to devote himself to rebuilding his motherland, Bohai, which is threatened by the Khitan. In the process, he is involved in a love quadrangle. Yoon So-yi, who showed off her dazzling martial arts in the movie "Arhat Palm Wind War", will play the role of Yan Suhe, the first female warrior in Bohai. She wanders between two men and interprets a love tragedy. After Yan Suhe's parents were killed by Khitan invaders, she was raised by a secret organization with strong martial arts. She is a martial arts expert and has unique kung fu. She was ordered to find the exiled prince in a critical moment. In order to protect the prince, she took out the shadowless sword. During the more than ten years of exile, Daejeong-hyeon was a civilian who made a living by reselling stolen goods. Because he had to face the great changes in fate and decades of exile, he did not trust Yan Suhe and did not believe everything she told him, so he chose to escape. On his way to escape, he encountered a group of assassins sent by the invaders. Fortunately, with the help of Yeon Su-ha, he barely escaped death, and then decided to return to Bohai with her. The role of Jun Heon-pyeong, who competes with Dae Jung-hyun for power and love, is played by Shin Hyun-jun, who left a strong impression in "Flying Dance". He was originally a general of Bohai, but because of his greedy ambitions, he betrayed his homeland and colluded with the Khitan invaders who promised to help him establish a kingdom. Can Dae Jung-hyun and Yeon Su-ha break through the siege and return to Bohai smoothly? An inevitable bloody battle unfolds...