Kuba, Basia, and their younger brother Tom have always loved puzzles. In the summer, they spent whole days on their bikes, scouring the surrounding forests and ruins. One day, when the sun was already hiding behind the horizon, Basia glanced at her grandfather's map and pointed with her finger at an abandoned mine, which - as the town elders rumoured - should not be approached after dark. "Why don't we go there?" - she whispered, and her eyes shone with excitement. Cuba immediately agreed, because he had always wanted to find out whether the old legend of the Strange Miner was just a figment of his imagination or something more. They arrived at the site just as the sky had turned a deep garnet. The old mine gate stood ajar, and a strange, almost invisible glow came from inside. Tom squeezed his torch tighter. "After all, there's no electricity in there!" - whispered Kuba, but Basia was already taking her first steps into the dark corridor. Their shoes creaked on the damp boards and the air seemed to grow colder and colder. Some shadows flashed on the walls. At one point Tom's torchlight suddenly went out. Everything around them sank into darkness. After a while, they heard a rustling and a very quiet, drawn-out sigh somewhere from the depths of the corridor. Then a mysterious light appeared in front of them and moved towards them, flickering like a lantern.... The children froze in place, unsure whether to run away or go on.