Han Seo-jun, a 29-year-old private detective in Seoul, accidentally frees Yoon Hwa-rin, a nine-tailed fox spirit, and merges souls with her to survive a deadly curse. Now sharing his body with the mischievous spirit, Seo-jun gains supernatural powers and transforms into a beautiful woman. As they investigate dangerous supernatural cases, they uncover a conspiracy threatening to open a gate between the human world and the Spirit Realm.