Marenka and Ronja - The patent part 7 of 7

Marenka is the chief secretary in a mechanical engineering company. A new machine control system was developed and patented here.

One afternoon her doorbell rings and a fitter is at the door. She lets him in and experiences a nasty surprise. The stranger overpowers Marenka, ties and gags her. Then he coerces Marenka to order her colleague, the management assistant, Ronja to join her. When Ronja rings the doorbell, she has no idea what will happen.