Veterinarian Anastasia Bukova finally managed to go on vacation away from her cows. He found nothing better than to visit his friend Avvakum Zakhov, who was languishing from loneliness. He is still deeply “preserved” and brightens up his dreary everyday life with his passion for cinema and photography and evenings with Doctor of Physical and Mathematical Sciences Nayden Naydenov, a permanent resident of a wheelchair. Zakhov and Naydenov were united by loneliness and a love of solving puzzles, anagrams and all sorts of intellectual riddles. Sometimes the professor is visited by his nephew Kharlampiy, a successful master of setting up shop windows and exhibition pavilions, as well as a lover of card games, and his bride, the “beautiful fairy” ballerina Maria Maksimova. Meanwhile, in the border sector L-Z, a group of saboteurs attempts an armed breakthrough. While the border guards are localizing the breakthrough, an unknown person makes his way to the Momchil-2 border defensive structure and takes photographs of it. From the intercepted ciphergrams, the Bulgarian state security finds out that the enemy spy has not yet handed over the obtained material to his foreign masters. The place and time of the transfer will be indicated by a special code, and how quickly it can be solved will determine whether or not the counterintelligence officers will be able to prevent the transfer of secret information to the enemy. But bad luck (or malicious intent?) - the main cryptographer gets into an accident. And then Colonel Manov decides to involve Professor Naydenov, who has performed similar tasks before, for decryption. Avvakum Zakhov again finds himself in the thick of things.