Katerina's grandfather lives on the top floor of a LARGE apartment building with locked doors, closed windows, and wide balconies, always deserted and silent. But one day, Katerina's ball falls onto the lower balcony... "Who could possibly live there?" wondered Mr. Andreas. "We'll find out right away!" said Katerina decisively, and, pulling her grandfather by the hand, they quickly went down to the lower floor. The doorbell read...