Act I opens in the Stockmann family house shortly after supper time. Billing, the sub-editor of the local paper People’s Messenger, is eating roast beef with Mrs. Katherine Stockmann. He was supposed to eat with Dr. Thomas Stockmann, but Billing was late, and the doctor did not wait for him. Instead, Thomas ate at the planned time and left with their sons Morten and Ejlif. As Billing eats his meal, two other guests arrive at the house. The first is Thomas’s brother Peter Stockmann, the local mayor. Next comes Hovstad, the People’s Messenger editor. Katherine offers the men some roast beef. Hovstad accepts, but Peter says that eating meat in the evening will upset his stomach.

Billing and Hovstad have come to the house to talk to Thomas about the Baths, a recently built medicinal spa that everyone hopes will make their small town famous. Thomas and Peter are both instrumental in running the Baths; Thomas is the medical director and Peter is the chairman. Since summer is approaching, the editors hope to publish a piece that Thomas wrote a few months earlier about the Baths, which they hope will entice potential clients will be to visit the town.