The story revolves around Choi Kang-chi (played by Lee Seung-gi), a half-human, half-gumiho (mythical nine-tailed fox) who was raised by a human family after being abandoned as a baby. Kang-chi is unaware of his supernatural heritage and struggles to fit in with humans while dealing with his monstrous abilities.
As Kang-chi searches for the Gu Family Book, he crosses paths with Dam Yeo-wool (played by Suzy), a skilled martial artist and member of the righteous group known as the Damo. Yeo-wool becomes Kang-chi's love interest and the two embark on a journey together, facing numerous challenges and enemies along the way.
The series delves into themes of love, loyalty, betrayal, and self-discovery as Kang-chi learns about his true identity and confronts powerful foes who seek to use the Gu Family Book for their own nefarious purposes. The plot also explores the complex relationships between different characters, including Kang-chi's human family, his fellow martial artists, and various political factions vying for power. Throughout the series, Kang-chi must navigate the dangerous world he inhabits while striving to protect his loved ones and fulfill his destiny.