The Mystery of Apartment Number 13

In the center of Kaliningrad, during excavations of the former Royal Castle, a group of archaeologists finds a silver box with unusual items and inscriptions, belonging to a certain Paul Skalich, an alchemist and necromancer of the 16th century…
It would seem that for a quartet of brave detective guides from Moscow, a trip to Kaliningrad should be just an ordinary school competition. But instead of excursions and walks, Yana, Marina, Polina, and Miron are faced with a case involving amulets, secrets, and ancient curses. They must help a girl named Masha solve the mystery of the symbols on the walls, decipher the message on the Stone of Lies, find a secret mechanism in the old Kurhaus, and much more... In short, schoolchildren of the smartphone age become detectives once again!

An exciting mix of mysticism, adventure, and detective work on the streets of Russia's most mysterious city. The second case is open.