The Question and Answer section for Number the Stars is a great resource to ask questions, find answers, and discuss the novel.
A German soldier knocks and demands to know why so many people have gathered at the house.
I'm assuming you are referring to chapter 1. We see that the novel is during WW2 and the German occupation of Denmark. We also find out about the persecution of Jews in Denmark by the Nazis.
They came into the house and ripped the baby pictures of Lise in half as will as being loud and waking up the girls.