Strange Neighbour

Since the strange and spooky neighbor Gertrude Tappendiek moved in, nothing is the same as it used to be. During the day, whimpering noises and foul smells emanate from their apartment, and at night, pets in the neighborhood disappear. What's happening? What is the talk of occult rites and offerings? You want to get to the bottom of the matter. You know that Gertrude Tappendiek always leaves the house at the same time and comes back exactly one hour later. You gain access to her apartment, but suddenly the door slams shut and can no longer be opened. Can you figure out a way to not become a victim yourself?