The setting of Act III is the Gardner home, where Praed and Crofts have spent the night. It is late morning and the Reverend Samuel Gardner comes outside to find Frank reading the newspaper. The Reverend has a hangover, having stayed up late drinking with his two guests. Frank tells him that Mrs. Gardner and Bessie, one of Frank's sisters, have gone into town in order to avoid meeting Mrs. Warren, who will be arriving at the house shortly. As Reverend Samuel Gardner excuses himself, Praed enters and scolds Frank for treating his father with disrespect all the time.
Mrs. Warren and Vivie arrive, and the Reverend Samuel Gardner goes to meet them nervously. He leads Mrs. Warren and Crofts on a tour of the church and rectory grounds, leaving Frank and Vivie alone together. Vivie and Frank discuss Mrs. Warren. Frank makes fun of her, calling her "an old wretch" (77) and scolding Vivie for pretending to get along with her. Vivie, however, insists that he show her mother more respect.
Frank and Vivie's ensuing conversation is flirtatious in a specific way: they play at being children with each other. Vivie wonders if their game is strange, but they decide it's not since neither of them played house in this way as children. Crofts returns to the scene, interrupting their flirtation. He asks Frank to leave.
Crofts proposes marriage to Vivie, using the same commercial justification he used with her mother the night before. Whereas Mrs. Warren reacted negatively to this approach, Vivie assures Crofts that she understands and appreciates it. However, she still rejects him, since she does not wish to marry anyone. Crofts does not take her "no" easily, and continues to try to convince her to say yes.
In trying to convince her to marry him, Crofts inadvertently reveals to Vivie that her mother is his business partner. Upon learning that Mrs. Warren continues to operate brothels, Vivie becomes sickened. Crofts doesn't understand her reaction, and continues to discuss his and her mother's business as if it were a reason for her to marry him, rather than a reason for her to separate herself from both of them.
Vivie tells Crofts that she knew about her mother's profession already, accusing him of wanting to withhold it from her until they were married as a way to break her spirit and manipulate her. She tells him she is disgusted with his work, since unlike her mother, he chose it for the profits. Crofts laughs at her for being naive about where money comes from in the world; in fact, the money that supports her own lifestyle comes from his and her mother's work. She tries to leave and he stops her, so she rings the bell on the gate.
Frank appears immediately, having been listening the whole time. He carries a rifle and points it at Crofts, but Vivie tells him to put it away. Before exiting through the gate, Crofts tells Vivie and Frank that they are half-siblings. Frank is still pointing the gun after Crofts, and Vivie puts it to her own chest, telling him to fire. Frank drops the gun and tries to continue their flirtation, but Vivie is disgusted now and leaves to return to the city. Frank runs after her.
The relationship between mother and daughter has changed in Act III, with the former disrespect Vivie showed her mother now reflected in Frank's attitude toward his father. Frank comes off as resentful and childish in both cases. Praed scolds him for making fun of the Reverend Samuel Gardner, on whom he is financially dependent, and Vivie demands he show more respect to Mrs. Warren. Her attitude toward her mother has changed because, the night before, Mrs. Warren revealed her sympathetic history to her daughter.
Vivie and Frank's friendship is revealed as close and flirtatious, if a bit strange. The way they flirt with each other is to pretend to be children, as if they are playing house. They admit that neither of them played this way when they actually were children, suggesting that this kind of interaction is a coping mechanism for something that was absent in their childhoods. Whereas Vivie had shut down Frank's advances the night before, now that she has reconciled with her mother, she is more open to flirting back. However, after Crofts suggests that they are half-siblings, Vivie's interest in this particular flirtation turns cold. She tells Frank, "You make all my flesh creep" (85) before leaving.
Croft's marriage proposal serves to highlight the difference between Vivie's approach to marriage and that of her mother. Whereas both women reject the idea that Crofts should marry Vivie, Mrs. Warren's rejection is based in repulsion at such a commercial approach to marriage. Vivie, on the other hand, tells Crofts that she appreciates how "business-like" (79) he is about the offer. However, she rejects him based on personal preference.
In this act, Crofts reveals to Vivie the rest of Mrs. Warren's secret regarding her profession: she continues to run brothels. Upon learning this new information, Vivie no longer understands her mother's point of view and judges both Mrs. Warren and Crofts harshly. In asking her to keep the secret from others, Crofts invokes convention and the judgment of others: "Since it's been a secret so long, it had better remain so" (81). The dramatic irony at play here is that Crofts does not know the damage he has just done to the relationship between Vivie and her mother by revealing the rest of this secret.
The idea of morality comes into question on a large scale during Crofts argument with Vivie in this act. She accuses him of being immoral for operating brothels purely for the sake of profit. In response, he chastises her for assuming that there is any honest way to make money. He insists that everyone "in decent society" (83) operates immorally in order to maintain status. The irony of this statement is not lost on Vivie: if everyone in the upper echelons of society is immoral, how can they see themselves as above those people who, like Mrs. Warren, turn to prostitution or other "immoral" work to survive?