The setting is a large hall in Captain Horster's house. It is crowded with townspeople. A number of them are discussing the meeting, and they decide to watch how Aslaksen responds to the issues presented. Billing is there to cover the meeting for the paper. Horster leads in Mrs. Stockmann and the children and sits them close to the door, so they can exit quickly if need be. Hovstad, Aslaksen, and Mayor Stockmann enter and take up different positions around the room. Dr. Stockmann enters to tentative applause and hissing. Aslaksen quickly motions that a chairman be appointed, and he is quickly elected to be chair. The mayor immediately moves that Dr. Stockmann not be allowed to read his report or talk about the baths, whipping up support from the crowd. He and Aslaksen work together to convince the crowd that the doctor is out to harm the town's best interests. Hovstad joins in and talks about the welfare of the Stockmann family. The motion passes.
Dr. Stockmann is angry. Just as he is about to speak, a drunk wanders in and demands for his right to be heard, but he is quickly ejected. Not permitted to speak about the pollution in the baths, the doctor begins to speak about the pollution in the towns. He talks of how he conceived the idea of the baths because he wanted to work for the people. But then, he says, he realized the "colossal stupidity of the authorities." Aslaksen tries to quiet him, but he continues. He is talking about the failures of his brother the mayor, when the drunk enters again and is quickly thrown out. The doctor continues, saying that the authorities are not the worst enemies. The worst enemy, he says, is the majority. The crowd goes wild with anger. Aslaksen urges the doctor to back his remarks. The doctor says that stupid people are in the majority and that power should lie in the hands of the minority. He says he does not advocate aristocracy, but for the intelligent, freethinking minority. He says the idea of the common, crass majority being in the right is an outdated truth. He asks Hovstad if, being another freethinker, he doesn't agree with him, but Hovstad merely shouts that nowhere in print can it be proven that he is a freethinker. The doctor continues, comparing the masses to mongrels and the intelligent minority to purebreds. He attacks Hovstad for not agreeing with him, and Hovstad shouts out that he is descended from peasants and believes in the people. The doctor sums up by saying that morality and freethinking go hand in hand. He insists that his message will be heard and threatens to write to newspapers in other towns.
Hovstad declares that the doctor must be an enemy of the people, and, in his excitement, Dr. Stockmann agrees, urging that the town should be wiped out, that vermin should be destroyed. Aslaksen proposes that the meeting declare the doctor "an enemy of the people." While Aslaksen is collecting the votes, Billings explains to several men that the doctor often drinks and that he had recently been denied a raise. Morten Kiil approaches the doctor and says that if his tanneries are implicated in bad publicity about pollution, the doctor may suffer. Aslaksen announces that by a unanimous vote Dr. Stockmann has been declared an enemy of the people. He leaves with his family, as the crowd chants "enemy."
This act represents the climax of the play. We see Dr. Stockmann at his most impassioned and the rest of the town at its most conservative and conspiratorial. The men who were having dinner at Dr. Stockmann's house in the first act are publicly denouncing him, and he is denouncing them.
The doctor's point about the tyranny of the majority is complex. It is certainly not Ibsen's invention. The English political philosopher John Stuart Mill wrote along similar lines earlier in the nineteenth century. It would be hasty to assume that Dr. Stockmann is speaking Ibsen's own ideas. However, Ibsen was certainly eager to express his frustrations with rule by majority in the wake of the liberal media's condemnation of his previous play, Ghosts.
It is ironic that the doctor chooses to speak on the tyranny of the majority in front of a crowd of townspeople. The mayor probably also believes in the rule of an intelligent minority, and he maintains it by conspiring with others that he deems part of the worthy minority. Dr. Stockmann's vision of rule by the minority is different from the mayor's. The doctor sees that although people like the mayor and Hovstad are technically in charge of the town government or the newspaper, they are still subject to the opinion of the masses. The mayor really has no choice but to oppose the doctor's proposal for the baths, because he is the tool of the masses, and Hovstad could not support the doctor if he wanted to because he is subject to the demands of his less freethinking subscribers.