Twelve-year-old Mia and her classmate Benny take a class trip to the Gruber Family's mountain ranch, where they begin to suspect something's fishy: Mysterious witching symbols appear, the Gruber's cattle falls sick, the well water turns black and the barn burns down. What the heck is going on here? Are they being haunted by an evil mountain spirit? Or is someone trying to put the Grubers out of business? Mia and Benny get unexpected support from their new classmate Johannes. Together they follow their handful of clues and leads: How did the poison the kids found wind up in the stable? What is the new cook hiding, and why? And what about the Mayor, who wants to get at the Gruber's property? Young Luca Gruber blames himself for trying to find the fabled Hoard of the Black King up on the mountain. Did he bring the curse of the Black King on his family? But Mia is too sensible to believe in fairy tales...