When their parents go to America for the summer, Madlyn and Rollo are sent to their great-aunt Emily and great-uncle George at Clawstone Castle, home of the legendary and mysterious Wild White Cattle of Clawstone Park. But times are hard at Clawstone, as the fancier castle down the road attracts all the tourist traffic. Determined to save the castle and the herd, Madlyn and Rollo audition a cast of ghosts to add some thrills to the Clawstone tours, and soon visitors are pouring through the gates. But just when things are looking up, the ghosts and children find themselves facing a great mystery, and some very sinister enemies. Will Madlyn, Rollo, and their ghostly friends find a way to save the day?