William and Abigail live in a castle in Gladbeki, where coal—the so-called "black gold"—is considered the key to prosperity. But their homeland harbors dark secrets. A mysterious friend from a distant land takes them on a journey that leads them deep into their country's past and future. In their search for answers, the siblings ask themselves whether coal can really bring the prosperity they hope for, or whether it casts a dangerous shadow. The historical background of the coal industry, coupled with a captivating adventure, makes this novel a thrilling reading experience.