In the reading room of the library, St. Petersburg of the 19th century comes to life: participants in the detective quest gradually unravel a chain of real high-profile cases, searching for clues among the bookshelves and taking on the role of detectives. This is a game for those who love puzzles, historical details, and the intellectual thrill of investigation. In the library on Karpovka, the detective turns into a game of the mind. Instead of a dry account of the history of urban detective work, guests are invited to be part of the investigation: in their hands are fragments of cases, newspaper clippings, and hints at connections between seemingly separate episodes. Gradually, it becomes clear that all these stories form a clever combination, and it is this that needs to be unraveled. The organizers rely on real high-profile cases from the second half of the 19th century. Participants learn how the detective police operated, what methods the city guards used, how testimonies and evidence were recorded, and what details could reveal a suspect long before official protocols appeared. Instead of a textbook, there is a game space where every detail of the surrounding environment can be a significant clue. The format will especially appeal to those who are tired of standard quizzes. Here, it is not about recalling correct answers, but about building theories, debating, testing hypotheses, and admitting mistakes. The course of the investigation depends on how carefully participants read the texts, compare facts, and notice contradictions. This approach trains observation skills, logical thinking, and teamwork. In the end, teams compare their theories with real historical facts and discuss why the detective police made such conclusions. This is a rare case where leisure format merges with careful work with sources: after the game, one wants to reread the city chronicles, pay attention to memorable places, and return to the library for new investigations.