Petka is a little microbe boy. He not only saves his home water droplet from an ant but also befriends the youngest research assistant. Anginchen, who lives in the third ice cream cup, is also his friend. When Petka discovers that he can make kefir from milk, he is determined to work in a dairy. However, he is still too small. Will he succeed in convincing his parents and the dairy director of his idea?.