Act IV opens with Berta, her eyes rimmed with red, lighting a lamp against the evening gloom. Aunt Julia comes to the house and tells Hedda that Aunt Rina has died. She laments the passing of her beloved sister, but says that the old woman died peacefully. Hedda asks Julia if there is anything she can help her with, but Julia protests, saying that she wouldn't think of it. She also makes yet another reference to Hedda's supposed pregnancy, saying that it is not the time for her to be bringing "misery" into Hedda's house. When Tesman asks Julia what she plans to do next, she says that she might move another sick person into Rina's vacated room. Julia also implies that she may move in with her and Tesman once Hedda's child is born. Hedda reacts to the idea with revulsion, and Aunt Julia exits.
Once alone with Tesman, Hedda remarks that his aunt's death seems to be affecting him even more deeply than it is Aunt Julia. Tesman, however, tells her that he is simply preoccupied - he went over to Eilert's house to tell him that the manuscript was safe and sound, but Lovborg was nowhere to be found. He then ran into Mrs. Elvsted, who told him that Lovborg had been to their house in the morning, and had said that he had torn the manuscript to shreds. Tesman asks Hedda if she told Lovborg that she had the manuscript, but Hedda replies that she did not. Tesman says that he must return the manuscript immediately, but Hedda reveals that she herself has burned the pages. Tesman screams out in horror, asking his wife how she could have committed such a blatant crime. Hedda tells him that she did it because she knew he was jealous of the work, and she didn't want anyone to overshadow her husband. Tesman becomes ecstatic at the idea that his wife might love him after all, and is also overjoyed when Hedda refers to him as "George" - presumably she rarely calls him by his first name. Hedda, for her own part, is utterly repulsed by his happiness, and says in despair, "I can't stand this."
In the fourth act, the play comes full circle. Whereas we opened with sunlight bathing the drawing room and a lively young couple returning from their honeymoon, it is now evening, and the atmosphere is one of funereal darkness. At the same time, the sense of possibility that characterized the play's first act - Hedda was in a new marriage, and a new home, and pregnant with her first child - has now given way to a sense of stifling inevitability. Now that Aunt Rina is dead, it seems certain that Hedda will be burdened with two new housemates: an infant child and an elderly woman. She will be stuck in a loveless marriage, raising a baby she seemingly has no interest in, and fussed over by a woman for whom she can barely hide her revulsion.
One of the biggest mysteries of Hedda Gabler is why, exactly, Hedda burns Lovborg's manuscript. It is possible that she simply wants to destroy the "child" that has sprung from Lovborg and Mrs. Elvsted's relationship - and indeed she witnesses the two of them referring to it as such, Mrs. Elvsted saying that she feels as though he has killed their child, and Lovborg confiding to Hedda after Mrs. Elvsted's departure that he is as distraught as if he had lost his offspring. However, it would be inconsistent with Hedda's character to be motivated by such a trivial concern. It is also possible that Hedda sees the book as yet another one of society's puppet strings, keeping Lovborg tied to a circle and a life he wants to be freed from. Throughout the play, Hedda's machinations are intended to free people from the societal bonds that restrict them, alerting them to their deepest desires. Indeed, Hedda seems to see Lovborg as very much like herself: he cannot seem to find happiness in the conventions of life. Lovborg's alcoholism is what separates him from society, but it is also an integral aspect of his character, and perhaps Hedda believes that by burning his book, she is setting him free.
The unfortunate consequence of this, however, is that she must somehow account for her actions and frame them in some kind of socially acceptable light. Even though it is likely that even Hedda herself does not understand why she burned the book - on a conscious level, at least - she must explain to her husband why she did so. Tesman is aghast when Hedda reveals to him what she has done, but she quickly turns his mood to one of joy by insisting that she did it for him, so that he would not be overshadowed by his rival's success.
Tesman's career, of course, is the last of Hedda's concerns, but her rationale certainly pacifies her husband. In fact, he is so thrilled that his wife is finally showing him some affection that he's tempted to tell everyone on earth of his wife's grand gesture. Hedda, of course, is utterly mortified at this idea - her husband is threatening to reveal her act of liberation as an act of self-sacrificing devotion. Hedda can't bear the idea, and it is this that precipitates her final decline.