St. Basil's Cathedral is a true treasure of architecture and scientific thought of Russian architecture of the 16th century. But few people know that a great secret is hidden within the walls of the cathedral, which only a select few can solve... In St. Basil's Cathedral, right during the excursion led by guide Elena Sinitskaya, one of the visitors dies. He dies under strange circumstances next to the grave of St. Basil, and Lena gets the impression that he was looking for something there. And the next day it turns out that Professor Plotnikov, Sinitskaya’s scientific supervisor, who was studying the era of the reign of Ivan the Terrible and the architecture of the 16th century, was killed. Before his death, Plotnikov managed to write some kind of code on a piece of paper...