The play starts in the home of the main character, Dr. Stockmann, who is now having a guest. His guest’s name is Mr. Billings and he works in the local newspaper. Mrs. Stockmann, who is also present, hears knocking at the door and suggests that the editor of the newspaper, Mr. Hovstad also decided to come. But it isn’t Mr. Hovstad, but the Mayor of the town and her brother-in-law. Mr. Billings, confused by the visit of his boss, reports that he has a business conversation: Dr. Stockmann is writing the new article for the newspaper. The previous one was about the new baths that are going to be opened in the town and their value for health. Mayor agrees that the baths are valuable not only for the health but for the town’s prosperity, because they will attract tourists. He also corrects Mr. Billings that the idea of opening the baths belongs to him, not to his brother.
Another guest is brought inside by Dr. Stockmann. It is his old friend named Captain Horster, the brother of the Mayor. Captain greets everyone and says that now he has a wonderful life when he can afford meat and some small luxury items. He was stuck in poverty, but thanks to his brother, he now has a good job connected with the baths. The Mayor asks about the new article written by Dr. Stockmann, but the doctor replies that he needs to check some more facts before announcing the article. The Mayor demands to tell him everything immediately, because he wants his baths to be presented in a best way possible, but Dr. Stockmann firmly refuses. Enraged, the Mayor leaves the house.
Comes Hovstad and secretly tells that the Mayor dislikes his newspaper for being too liberal, especially before the election coming soon. Mayor wants the newspaper to support him, but Hovstad stays independent. Petra Stockmann, the daughter of Dr. Stockmann, returns from the school and tells her father that she picked up a letter for him. Dr. Stockmann is visibly glad and leaves to read the letter alone. Mrs. Stockmann explains that her husband was waiting for so long for this letter.
Petra tells the guests that to her, as a teacher, is becoming harder and harder to teach kids when they learn so many lies outside the school. She hopes to open her own school one day. Captain Horster listens to her and suggests that she can use the ground floor of his old house that stays abandoned. Captain Horster is going to depart to America soon so he will need someone to care for it. Hovstad interrupts saying that Petra can have a prominent career as a journalist and asks about the translation of a novel she promised to complete. Petra says that it’s almost finished.
Dr. Stockmann returns and seem to be very worried and excited at the same time to receive the letter. He tells the guests that he is close to making a discovery: the bath that are so highly praised and advertised are not useful for health, they are actually poisonous. The letter contains information about the pipes laid too low to be safe from the waste of the tanning factories nearby. All the winter Dr. Stockmann was studying the case trying to find out if the water of the baths is really poisoned: he sent the samples of it to the several major universities and finally received the results - all the water pipes have to be relocated or the epidemic will start amongst the baths guests. Now he rejoices, because when he tried to warn the town administration they blatantly told him he’s out of his mind. But with such adamant proofs they won’t have the choice except to relay the pipe system and give Dr. Stockmann the credit he deserved.
Dr. Stockmann asks Petra to send the note to her grandfather, who was very sceptical about his research and himself prepares an announcement to the Mayor. Hovstad, smelling the sensation, wants to make the short note about his work in the newspaper, thinking that the city should know who is the hero that saved everyone from disease and disgrace. Dr. Stockmann humbly replies that he is happy just to serve such a lovely city and its dwellers.
Soon Dr. Stockmann receives a reply from the Mayor, where he asks to come at noon. Old Morton Kiil, Dr. Stockmann’s stepfather, still remains sceptical. He says that Dr. Stockmann played a good trick to the Mayor - something that his stepson doesn’t understand. Old Morton Kiil explains that what causes the disease - bacteria or something else - is invisible, so no one would believe it is here. When he hears about Hovstad, he decides that it is just a conspiracy for discrediting the Mayor before the election planned by Dr. Stockmann and Hovstad’s newspaper.
Old Morton Kiil storms off the house and Dr. Stockmann is left thinking about the fact that people indeed may not believe him. Hovstad says that the poison isn’t only in the pipes, it is already in the minds of the people overwhelmed with bureaucracy and conspiracy theories. The excessive paperwork and lack of responsibility is the primary reason the pipes are laid in the wrong place. The town administration just didn’t care. Hovstad hopes that the case with the baths will show this problem to everyone and make people wake up and actually do something to fix it.
Enters Aslaksen, the printer from Hovstad’s newspaper. He tells that he is also a head of some social organisation that fights for their right and he is ready to support Dr. Stockmann. He offers to gather a peaceful demonstration in his support, but Dr. Stockmann, surprised, replies that the case is very clear and already proven, there is no need in the additional support. Aslaksen isn’t so sure, saying that usually the administration isn’t eager to react very fast to such issues. Aslaksen leaves and Hovstad continues persuading Dr. Stockmann that it is more of a political than medical case. Dr. Stockmann asks him to wait with the announcement in the newspaper until the case is discussed with the authorities. Hovstad leaves and Dr. Stockmann reflects about feeling good after such an exhausting but useful work.
The Mayor comes in and starts from the practical question: does Dr. Stockmann know how much the new pipes will cost and how long the work will take. Mayor says that the town will lost sixty thousand dollars and two years without working bath. Moreover, if the cause of the maintenance becomes known, no one will come to the baths anymore. It will disrupt the economy of the town and ruin it. Mayor angrily adds that Dr. Stockmann solely will be responsible for all this disaster. The Doctor is shocked but stays adamant: the baths are dangerous and they just can’t stay the way they are. Mayor doubts that the danger is so big: he says that Dr. Stockmann panics too much and maybe the water can be purified without relaying the pipes. But the Doctor answers that everything except changing the pipe system will be a crime against the people attending the baths, the society and conscience itself. He is sure that the Mayor is just afraid to look incompetent, not that he is ready to sacrifice people to earn money. They argue and the Mayor forbids Dr. Stockmann to publish the note and to study the water in the baths any longer. The Mayor demands obedience as an authority, but the Doctor angrily replies that he is morally obliged to publish his discovery and prove that he is right, both to save the people from contamination and the society from lie and fraud. The Mayor warns him that such disobedience will have consequences and Dr. Stockmann will end up as an enemy of the whole society. But Dr. Stockmann believes that he is right and people will support him, because he is telling the truth. When the Mayor leaves, Mrs. Stockmann quietly reminds her husband that he has a family that he have just endangered by his arrogant behaviour with the Mayor. But the Doctor says that he will do what he has to do or, otherwise, he will never be able to look in the face of his sons.
The action shifts to the editor’s room of Hovstad’s “People’s Messenger”. Hovstad and Billing are talking about the article of Dr. Stockmann. They are going to use it to discredit the Mayor before the election and they hope that the new Mayor will be a person with more liberal ideas. Dr. Stockmann comes and says that he had a talk with Mayor and they can publish the article. Aslaksen enters and joins the discussion, he assures that no one will be offended and all the intelligent and honest people of the town will understand the Doctor correctly. Dr. Stockmann himself starts to believe that his article will trigger the great changes for better life, but Aslaksen calms him down, saying that the authorities can strike back, so they have to be cautious at the beginning. Billing declares with pathos that Dr. Stockmann will be remembered as “The Friend of the People”.
Dr. Stockmann leaves with Aslaksen and Hovstad leaves to think where they can get some money to be supported. Hovstad thinks that Old Mortal Kiil can leave some heritage to Dr. Stockmann. Petra comes in, apologizing for not translating the novel Hovstad asked her, because she feels that the novel is a lie and it doesn’t suit Hovstad’s liberal ideas at all. Hovstad tells her that the newspaper needs such things to entertain people and make it interesting to read, so that they will also read the more liberal texts in it. Petra is clearly disgusted with such approach. She feels that Hovstad have changed and she can’t trust him anymore.
Petra leaves and Aslaksen returns, saying that the Mayor came here and is in the office now. Mayor, pretending to just see his friends, enters and sees the article of Dr. Stockmann. He asks if they are going to print it and eloquently explains that doing so will have the devastating consequences for all the town. The poor people Hovstad is so eager to support will be the first ones to suffer, because the money needed for pipe maintenance will be taken from their taxes. Both Aslaksen and Hovstad are confused and shocked. They think that Dr. Stockmann just didn’t think it over or didn’t have enough information. Mayor gives them a short note about the small maintenance he offers to cleanse the water in the baths and asks them to print it instead.
Dr. Stockmann returns to ask some more questions about his paper. The Mayor hides in the next room. The Doctor asks if the article is ready to print, but confused Hovstad says that it will take more time. Dr. Stockmann, understanding that something isn’t right, warns him that there will be possible attempts to discredit his study. Mrs. Stockmann comes in to plead her husband to stop again, saying that he should care about his family first. The Doctor suddenly notices Mayor’s hat and comes for him. He blatantly tells him that he will do what he decided to do, but to his shock, Hovstad and Aslaksen take the side of the Mayor. They explain Dr. Stockmann that the town’s reputation and economy will be ruined and the people will suffer. The Doctor replies that the silence will kill people also and states that the truth can’t be hidden. Hovstad tells him that no one will listen to him, because they won’t print the article. Than the Doctor promises to stay on the street and read his article aloud for the people to hear.
Dr. Stockmann arranges a meeting in the ground floor of Captain Horster’s house given by him to Petra. The people are puzzled and wonder why he decided to gather them. They look at Aslaksen as at their leader and decide to repeat everything after him. Everyone is here: Dr. Stockmann with his family, Aslaksen, Hovstad, Mayor and Billing. Dr. Stockmann starts to talk, but the Mayor interrupts, demanding an election of a chairman and other formalities. Confused, the Doctor replies that he is going to read a lecture about the poisoning, so no chairman is needed. But people listen to Aslaksen and elect him the chairman. Aslaksen teams up with the Mayor and says that the people don’t want the lecture about the baths. But Dr. Stockmann says that he isn’t going to talk about the baths, but about the other kind of poisoning and finally starts his speech.
He tells about that the very spirits of the people are contaminated, that they got used to listen to the lies, believe it and rely on it, not able to hear the truth anymore. Lie is the real poison that leads to any other kind of poisoning. He says that people don’t want to think by themselves anymore and act like a herd when they find a leader. They can’t stand anyone being free to make decisions and think. Dr. Stockmann finishes the speech with the statement that the town - and the country too - shall be led by the intelligent people, so if the majority are stupid and unable to think, anyone who denies the freedom of thought should be stripped of their voting rights.
The crowd goes mad. Dr. Stockmann is immediately proclaimed “The Enemy of the People” and everyone votes for it except the one man. Old Morton Kiil asks his stepson if his tannery is also to blame for the water poisoning. Dr. Stockmann says that not only his tannery poisons the water, it is one of the worst. Old Morton Kiil replies that this statement will cost him family fortune. Dr. Stockmann asks Captain Holster permission to sail with him to America and the Captain says that he has the room on his ship.
The action returns to the home of Dr. Stockmann. It is all messed up. The Doctor himself stands near the broken window holding the stone someone threw into it. He decides to save this stone as a reminder. The note from the owner of the house arrives: the Stockmanns have to move immediately. Petra comes in tears: she was fired from her school. The people don’t want to go against the common opinion and deal with “the enemy of the people” or his family. Captain Horster, who had to take the Stockmanns to America, arrives and tells that he lost his ship as a friend of “the enemy of the people”. The last straw is the Mayor coming to say that Dr. Stockmann is officially not allowed to go to the baths and he personally advises everyone not to give the Doctor a new job. He hints that Dr. Stockmann will be pardoned if he publicly states that he lied about the water contamination. The Doctor refuses. The Mayor accuses him of arrogance, because he knows that Old Morton Kiil is leaving him a huge heritage. Dr. Stockmann knows nothing about heritage, so the Mayor tells that Old Morton Kiil leaves a huge sum of money to Dr. Stockmann’s children and wife to live. The Doctor is relieved. Now he is sure that his family is safe and he can continue fighting for the truth. The Mayor accuses him of killing the town and Dr. Stockmann orders him to get out of his house, then asking his wife to scrub the floor where he was standing.
Old Morton Kiil enters and announces that he converted all the heritage of Dr. Stockmann’s family into shares of the baths. He is offended with Dr. Stockmann publicly announcing that his tannery is a source of pollution, so now he wants the Doctor to publicly clean his name, saying that that is not true. Otherwise the baths will be closed and the allowance for his family will turn into nothing. Dr. Stockmann is devastated with the news. He says that he needs to talk to his family and promises to give his answer at 2 PM.
When Old Morton Kiil is out Hovstad and Aslaksen come to visit Dr. Stockmann. They accuse him of being insincere with them. They think that he fabricated his study to have the shares of the baths drop and buy them at their lowest to sell them back after apologizing for the lie. Enraged, Dr. Stockman beats them with the stick and kicks them out of his house. He calls Petra and asks her to tell Old Morton Kiil that he isn’t going to surrender or leave the town. He will stand tall against all the odds and fight for the truth. If no one listens to him, he will found a school with his daughter and will teach the orphans and stray kids to think by themselves. He finishes his speech with the words that he learned an important lesson: the strongest man is the one who stands alone.