As Adam crossed the threshold of the school's biology lab, the clock had just struck twenty-two. During the day, the doors of this room were locked to the hilt, but today - thanks to Ola's skill at opening locks with a paperclip - there was an absolutely unofficial late-night visit. For Adam, Ola and their friend Michael, it was a last resort before tomorrow's biology test. Officially, of course, they came to practice identifying cells under the microscope. In practice... Well, that remains to be seen. The lab seemed more mysterious in the glare of the torches the guys were shining on the shelves cluttered with test tubes, organ models and piles of old notebooks. Ola glanced anxiously at the biology teacher's locker, which was rumoured to hold yeast mutants instead of coffee and a supply of toxic jokes for breaks. - Can you smell that? - Michael asked, wrinkling his nose. - It smells like... a grocery store in the old Praga district. Adam ignored his friend and walked over to a large aquarium standing in the corner. Instead of fish, he saw inside plastic pumpkins, a disco ball and... a jar marked "DO NOT OPEN! (Seriously.)". - 'I think we should open it,' Ola said, without giving it much thought. - Because after all, what could go wrong? All three of them approached, hesitated for another second, then Adam picked up the jar and turned the lid. At the same moment, there was a strange sound in the laboratory - something between the snoring of a hamster and the sound of a blender starting up. Suddenly, the disco ball began to glow with its own light, and a purple cloud of smoke rose from the aquarium. At that very moment, they heard footsteps in the corridor. Someone was very clearly approaching the laboratory door....