The Treasurer.

Ten-year-old Janek has a vivid imagination. He constantly makes things up and imagines himself as a superhero. When the demonic Utopiec replaces his older sister with the repulsive Podciep, no one believes him. To make matters worse, his parents send the sad and frightened boy on holiday to Silesia. Janek decides to rescue his sister from the world of demons, and his greatest ally turns out to be his eccentric great-grandfather, Marcin, a former miner.