Tale of the Nine Tailed follows the story of Lee Yeon, a legendary nine-tailed fox (gumiho) who once governed the Baekdudaegan Mountain Range as a mountain god. After sacrificing his position to resurrect the woman he loved, he has spent centuries living in the modern world, working as a civil servant who cleans up messes caused by supernatural beings that disrupt the human world. His life takes a turn when he encounters Nam Ji-ah, a fearless television producer who is determined to uncover the truth behind her parents' mysterious disappearance years ago. As their paths cross, Lee Yeon finds himself entangled in a dangerous game involving his estranged, volatile half-brother, Lee Rang, who harbors a deep resentment toward him. The series blends urban fantasy, folklore, and romance as the characters navigate ancient grudges, supernatural threats, and the complexities of fate, all while uncovering the dark secrets of the past that connect the human and spirit realms.