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

The Birlings are celebrating an engagement. It's a happy celebration that quickly turns sour with the Inspector's arrival and ensuing questions. He is attempting to chronicle the events leading up to a young girl's suicide, and the people in the room have a part in these events. His interrogations are public, not private; this gives the group a distinct discomfort as their personalities and actions come to light in front of the people who know and love them. Needless to say, the mood in the room moves from happy, to surprised, to accusatory, to horrified, to guilt ridden, in a very short period of time.