The Adventures of Petya and the Wolf. The Case of the Yellow Suitcase

In the realm of threes, an unusual epidemic is spreading: the heroes tremble at the sight of a sword, mermaids hide in the reeds, and house spirits have huddled behind the stove and abandoned their duties. It seems that the fairy-tale inhabitants have somehow caught the plague of fear...

Meanwhile, in St. Petersburg, another trouble has occurred: someone has stolen the yellow suitcase from the clumsy scholar, inside which was a wondrous medicine he had created, capable of curing any ailment.

Now Petya and the Wolf must unite once again and set off to find the kidnapper, as well as help the fairy-tale inhabitants rid themselves of their fears. Are these two incidents connected? And how can they persuade Baba Yaga's hut to get vaccinated?