Mr. Werle is giving a party in honor of his son's homecoming. Besides influential political friends, he has also invited Hialmar Ekdal, an old school fellow of Gregers. Feeling out of place and uncomfortable among the guests, Hialmar is more gloomy than ever when he overhears Werle whisper to Gregers that he hopes none noticed that they were thirteen at table. His friend however reassures him: Feeling more alien in his father's house than Hialmar feels, Gregers avers that he himself is "the thirteenth."
In another room, the servants reluctantly admit Old Ekdal. He explains that he has come to fetch some copy work which the bookkeeper left for him, and, unseen by the guests, he steals into the office.
Conversing with his old friend, Gregers is surprised to learn that Hialmar has married their former maidservant. Gina is a different person than the one he knew as a servant, young Ekdal explains; "she is by no means without culture" for "life itself is an education." He boasts that "her daily intercourse with me" has refined her "and then we know one or two rather remarkable men who come a good deal about us."
Thronging into the room, the chamberlains are joking with Mrs. Sorby who keeps up the witty repartee. Gregers advises his friend to join the conversation, but Hialmar does not know what to say. During a discussion about wines, he makes the guests laugh by asking whether vintages differ according to their seasons. As Werle involuntarily exclaims "Ugh," the guests turn to see the shabbily dressed Lieutenant Ekdal walk with the bookkeeper to the front door. Hialmar turns his back and faces the fireplace. When asked whether he knew that man, the son stammers "I don't know — I didn't notice" while Gregers recovers from his shock at old Ekdal's appearance. Reproaching Hialmar, young Werle says, "And you could stand there and deny that you knew him!" but the loudness of the guests interrupts their further conversation.
When Werle has a chance for a private talk with his son, Gregers shows deep bitterness toward his father. Accusing Werle of deceit in marrying off Gina to Hialmar, reproaching the lecherous behavior which caused his mother's death, Gregers concludes by blaming his father for ruining old Ekdal's life by framing him for the government swindle. Werle denies this last accusation. He tells his son that he should bury his past grievances and show filial approval for the intended marriage to Mrs. Sorby. It is not fair to his future wife to be a spectacle of scandal, and besides, they are well suited to each other. Gregers laughs scornfully. Never was there any family life in this house, he says, and now for the sake of Mrs. Sorby we are to set up a pretense of harmony, a "tableau of filial affection" to annihilate the last rumors "as to the wrongs the dead mother had to submit to." Pitying the gullibility of "poor Hialmar Ekdal" who does not realize that "what he calls his home is built up on a lie," Gregers says he will leave the house forever "for at last I see my mission in life."
Despite the brevity of this act, it lacks the intensity and tension that the introductory scenes build up in the previous plays. Ibsen quickly establishes all the relationships, however, and as he develops the history of his characters he shows which ones are "realistic" (old Werle and Mrs. Sorby, for instance) and which ones are tainted with "idealism" to cover their own weaknesses (Gregers and Hialmar Ekdal).
Mrs. Sorby appears in this act as a woman of the world. Although without status, she is able to treat her influential guests as equals and behaves with frankness (wittily implying that the chamberlains take graft) and compassion (ordering the servant to give "something nice" to old Ekdal to take home).
Hialmar Ekdal exposes his concern for keeping up appearances. At the same time he mourns his father's fallen position in society, he refuses to acknowledge publicly that he is related to the disreputable old man who intrudes on the high class party. Insisting that his wife is "not without education" Hialmar shows his status-seeking aspirations and proves that he has an inflated self-conceit.
The appearance of Lieutenant Ekdal at the party shows the audience his simplicity and lack of self-consciousness. He seems a creature from another world who merely stumbles blindly through those social spheres which include the chamberlains, Mr. Werle, and Mrs. Sorby. According to this scheme, Gregers and Hialmar, who each suspect themselves of being "thirteenth at table," inhabit a peripheral sphere which lies somewhere between the worlds of old Ekdal and old Werle.