It all started in the middle of a hot July, when the city seemed to sleep under the weight of the heat and the streets were deserted even in the centre of Kalisz. Marta never liked summers spent in the city, but this time they stayed with her brother because their parents had too much work. It was going to be a boring holiday until Igor turned up. Igor was the kind of outsider everyone knew, because for the past two years he had regularly turned up at various places with a notepad and a torch - even in broad daylight. On this day, they met him outside the abandoned 'Echo' cinema. He was sitting on a concrete pot and had a look on his face as if he had just thought of something brilliant. - Hey, what are you doing? - Marta asked, feigning indifference. - Have you heard about those tunnels under the city? - he chuckled without preliminaries, grinning. - I got a map from the city library. Old as the world. Who knows where it leads? Marta felt her heart start to beat faster. Kalisz was one of the oldest cities in Poland, but stories about undergrounds always sounded like something out of children's fairy tales. Meanwhile, Igor took out of his rucksack a yellowed piece of parchment with winding lines, strange symbols and markings on it. Adam, Martha's younger brother, looked on in disbelief. - 'Do you really want to go in there? Igor nodded. - Tonight. Are you with me? Before they had time to answer, they heard an unexpected sound from afar: someone creaked the old gate leading to the back of the cinema. All three of them stood still. A silhouette loomed in the semi-darkness. The stranger stood in the shadows and looked straight at them. The light from the lantern reflected in his eyes. For a brief moment, it seemed as if he wanted to say something, but he only raised his finger to his lips in a gesture of silence. - 'We meet at midnight,' whispered Igor, as if the silence was about to hear something. As they drove home, Marta couldn't stop thinking about the mysterious stranger and what - maybe - was waiting for them under the city streets. No one could sleep that night, and every second moved slowly towards the twelve o'clock hour. As midnight struck, the three teenagers stood outside the cinema again, and the shadow was already waiting for them, almost merging with the walls....