How does power shift as the action progresses in Act One and Act 2?

The Inspector’s power and insight into the situation is only really glimpsed, in this first act, by Sheila, who ominously predicts to Gerald as the curtain goes down that everyone will come to see that the Inspector knows far more than anyone realizes. Yet Priestley, in the first act, gives the Inspector no explicit moment of surprising the family by knowing more than they do. The level of tension in the play starts extremely low, builds gradually as the Inspector enters, and builds more as the characters come to understand the fate of Eva and their roles. Indeed, at the end of Act One, structured by Priestley so as to end on a point of tension, we discover that it is not just Birling and Sheila, but also Gerald, who is involved in Eva Smith’s demise. By the end of act one, we discover that the inspector carefully shifted control of the narrative. Birling has switched to the defensive and the others feel the heavy sense of implication in the crime. The inspector has the control going into act 2.