In order to avenge her family, Naeng Sowol has trained to be a special rank assassin her whole life. But before she completes her last mission, she is thwarted by Baek Woonbi, the heir of the most powerful faction in the martial world, who intervenes for his own plans. Despite their initial skirmishes, the two eventually agree to cooperate. It isn't long before their endeavors together stir up long-lost emotions inside Sowol... and reveal a truth that could change the martial world forever.