The Play opens in Dr. Stockmann's household. Mrs. Stockmann is entertaining the dinner guests. As the evening progresses the Mayor (also Dr. Stockmann's brother) and Hovstad (the editor of the newspaper) have come to the house. Dr. Stockmann and his two sons Ejlif and Morten have come home from a walk. As they all gather in the house, the Mayor needs to confront his brother about an article regarding the town health baths and the rumors that have been raised about them being contaminated. The Brothers get into an argument about their positions on hiding the truth and shaping the truth to get the results that are convenient. Petra (the Doctor's daughter) brings in the letter that her father has been waiting for. After Dr. Stockmann reads the letter, he discover his suspicions were right and the water from the baths is in fact contaminated. Hovstad now agrees to print the article and unfold the story. This will bring a great deal of attention to the baths and possibly will be the end of them (which will have repercussions on the town's economy). But Dr. Stockmann is overwhelmed with all that has happened and quickly believes he is the savior of the town.
The next morning in Dr. Stockmann house, Mrs. Stockmann gives the news to her husband that his brother Peter will stop by to talk about the baths. Meantime Morten Kiil (Dr. Stockmann's father in law) stops by the house to congratulate him on his discovery and what this will mean to the town. Hovstad and Aslaksen (the printer) stop by the house as well to reinforce their commitment to the doctor and extend their gratitude. The new alliance between the paper and Dr. Stockmann has a deeper interest than just the baths. The paper wants to confront the government of the town and expose the corruption that happens behind closed doors, and this opportunity is a way to start.
Peter (the mayor) enters the house, and everything becomes tense. Peter tells Dr. Stockmann that if he proceeds with this article and exposes this information to the town, he will be partially culpable for the ruin of the town. Peter accuses Dr. Stockmann of being selfish and not thinking of the bigger picture. He is encouraging Dr. Stockmann to retract himself from this article and to solve this problem in a more quiet way. The Doctor refuses his brother's propositions and the mayor reiterates that there will be terrible consequences for him and his family.
In the newspaper office Hovstad and Billing discuss the pros and cons of running Dr. Stockmann's article bashing the reputation of the government of the town. They are ready to proceed and help bring the privileged classes down. Dr. Stockmann comes into the office and tells them to print the article, but at this moment the whole office has a change of heart and are questioning how valuable is it really to expose the government and the town's baths in this way. They are realizing that printing this article will do more damage than help with the situation. Instead the paper is now on the side of the mayor, and has decided to print a statement of him talking about the baths and how good they are. Out of desperation, Dr. Stockmann decides that he doesn't need the paper to print anything and that he can fight this battle on his own. Dr. Stockmann decides to call a town meeting and spread the information that way. Mrs. Stockmann is present during all of this, and although she knows that her husband is making an extreme decision and is risking his reputation, she stands by his side.
At the town meeting in Captain Horster's house, Dr. Stockmann is about to read his water report to the townspeople. Billing, the family, the mayor, Aslaksen, and Hovstad are there. Aslaksen is elected the chair of the meeting to serve as a mediator. What ends up happening is that Aslaksen is trying to sabotage the doctor and stop him from communicating the report. When Stockmann finally gets a chance to speak, he talks about the contamination of the water but also gets into the town leaders and how they are the ones who know what is going on. He talks to the town about education and corruption too. The town feels insulted by these accusations and anger starts growing in the room. By the end of the meeting the town has rebelled as a mob against Dr. Stockmann and have marked him as an enemy of the people. Dr. Stockmann is exiled from the town.
It is the morning after at Dr. Stockmann's study. The windows of the house have been smashed. The town has turned against the family, and no one they know will help them. The landlord is evicting them from the house, and Petra got fired from school for having progressive opinions. Peter comes to the house to present Dr. Stockmann with a letter from the board of directors of the baths terminating his contract and a resolution from the householders association stating that no one should hire Dr. Stockmann in this town again.
On the other hand, Morten Kiil just bought an interest in the bath business. He expects that because his tannery is causing all the contamination, his son in law Dr. Stockmann will back off and let the issue go because now his family's money is also at jeopardy if he continues this battle. Dr. Stockmann refuses Morten Kiil's suggestions, and also ignores Peter's advice of leaving town for a few months. Dr. Stockmann has alienated everyone but stays true to his principles, even though he is standing alone. Dr. Stockmann knows that his family will always be by his side, and decides to accept his fate and become "the enemy of the people" if that is what it takes to do what is right.