Having quarreled with his son, Tsar Ivan the Terrible accidentally wounds him - as in the famous painting by Repin. The life of the prince is in the balance. To fix everything, Grozny wants to go back in time with the help of a magical grimoire. However, something went wrong, and Grozny finds himself in our time, where he meets the Osipov family. Nikita Osipov is an unsuccessful archaeologist and an equally unsuccessful father. He had long lost contact with the children - Romka and Polya. But now they are on a journey together to help Grozny find the grimoire and save the prince.