Lika Solomatina and Katya Oreshkina, anticipating a fun and carefree vacation, go to the provincial town of Gus-Frankovsk, to visit Katya’s grandmother. And grandma, by the way... is only eighteen years old. How can this be, you ask? Maybe, why not! But here’s what’s really incredible: upon arriving in the city, the girls find out that “grandmother”, a cheerful girl Svetlana, for no apparent reason committed suicide. This seems very strange and inexplicable to Katya. The friends decide to get to the bottom of the truth at all costs. But the more they engage in this mysterious matter, the more questions they have. What is the pagan sect of the “lurkers”? What secrets does Monastic Island hide? Who is Bluebeard? And finally, is Svetka really dead?! The girls, without hesitation, begin their investigation. But, as it turns out, someone clearly doesn’t want the young detectives to find out the truth...