In a small town, preparations for a theatre show are in full swing. The play on the program is based on a local legend about a huge treasure hidden deep underground. Many are those who wish to find it, but whoever sets out to look for it never returns. The protagonists of the performance are two sisters, Kacenka and Barborka, and musician Jakub, Barborka's jealous boyfriend. The theme of the play appeals to the greedy lord of the chateau Borivoj of Hájek, who comes with his brother Ignác, eccentric inventor and explorer. While somewhere underneath, at the real treasure, its three ghostly guards sit and devise all sorts of pastimes which do not please the Ruler of the Underground at all. His patience runs out when the bored guards interfere with the fates of the humans - making a bet about how the relationship between Jakub and Barborka will turn out.