How is the mood change when the Inspector first came in the Birlings' house?

The party is one in which the Birlings act as if things are "fine" when, in fact, they are only a reflection of the superficial acts in their lives. The celebration of the daughter's engagement is overshadowed by the son's drinking which they discreetly ignore. The fact that the family accepts so readily that Goole is from the police department hints at the fact that the "surface" of this family is not at all what is true. The fact that all have much to reveal in their complicity in the girl's death is not how they want to be perceived. The mood changes in that they do not want to be questioned, acting almost as if they are above the law.