The Spanish thriller series "Feria: The Darkest Light" tells the story of two sisters who uncover a horrifying truth about their parents. It turns out that their parents were involved in a terrible mystical ritual with irreversible consequences, resulting in the deaths of many people. Representatives of the Feria Civil Guard learn about this after visiting an old mine. Now, the sisters must come to terms with the new realities of their lives and the supernatural aspects that come with it.