When Brack arrives, Hedda immediately pesters him for details about the previous night's events. After leaving Tesman, she learns, the "inspired" Lovborg visited Mademoiselle Diana's "boisterous soiree" - an exclusive party to which he had been invited but had promised Brack and Tesman he would not go to because he had "turned over a new leaf." At the party, however, Lovborg's mood turned from merriment to fury when he discovered that his manuscript was gone. He began assaulting the women at the party, and the police soon arrived to break up the fracas. Lovborg resisted arrest, attacked one of the policemen, and ended up at the station.
Brack tells Hedda that Lovborg might use the Tesmans as a haven if he is shunned by the town, and encourages Hedda to close her doors to him. Brack also implies that he doesn't want Lovborg joining their new "triangle"; he fears that he will find himself "homeless" if Hedda allows Lovborg to take refuge with her. Hedda says that she feels as though Brack is threatening her, but Brack replies that he is not, he is merely saying that the "triangle ought to be spontaneously constructed." Brack exits, and moments later Eilert Lovborg arrives.
Hedda offers Lovborg no clues that she knows what happened the night before, but he seems extremely distraught. Mrs. Elvsted enters the room, and Lovborg tells her that their "ways must part" because he has abandoned his book and she can thus no longer be of "service" to him. Mrs. Elvsted is aghast and insists that she will not leave his side, but Lovborg is adamant. Lovborg says that he shredded the manuscript because he shredded his life to pieces, so it was only natural he should shred his work as well. Mrs. Elvsted leaves, devastated, realizing that she and Lovborg cannot have a future now: his reputation is ruined, and the possibility that his book could save it is now gone.
Hedda is left alone with Lovborg, who reveals the truth to her - that he's lost the manuscript. Lovborg implies that now he must kill himself, and Hedda encourages him to "make it beautiful." She tells him never to return again, and gives him one of her pistols "as a memento." He says that he recognizes the pistol - it was the same one she pointed at him years before - and says that she should have used it on him then, but she replies that he can use it now. Lovborg leaves, fully intending to commit suicide. Upon his exit, Hedda sits down by the fire and burns Lovborg's manuscript.
In Brack, Hedda sees a man whose thirst for control frightens even her. The moment Brack senses that Lovborg might become part of their new "triangle" he immediately threatens Hedda, saying that he will not protect the Tesmans if they fall into disrepute. Hedda says ominously, "I am heartily glad you have no power or control over me at all," and we immediately sense the subtext behind her words: for all of the lack of control Hedda has had in her own life, she fundamentally believes in free will - hence her obsession with pistols, which serve as a perpetual reminder that it is she who decides who lives and who dies.
There is, however, a rather sadistic game-playing element to Hedda's character that cannot be dismissed. In a sense, she sees society as a parlor game - one must behave and keep up one's reputation, all the while trying to conceal darker impulses and motivations. When one loses by succumbing to scandal or revealing these darker impulses or motivations, time is "up" and the consequences must be acknowledged. On one level, this explains her marriage - she "danced around" and tried different men until she likely saw that her reputation was at stake and had to marry Jorgen to remain a part of society. Even more, however, Hedda believes that the only natural option is death when scandal subsumes one's character. She puts an abrupt end to her scheming whenever her own reputation seems poised to fall into disrepute - for that would mean that she too would now have to check out of life's parlor game.
Hedda is a highly idiosyncratic character, but Ibsen nevertheless appears to view society's stiff repercussions for individuality with some disdain. In a sense, it is the opinions and perceptions of the community that seem to dictate all of the important decisions of an individual's life - when they marry, who they marry, when they have children, what they do for a living, how they live, and when they die.
Hedda, in her own way, seems to have declared herself judge, jury, and executioner, assimilating all of the necessary information and ushering people towards the realization of their deepest desires. The only character she can't seem to fend off is Brack, who seems even more intent on controlling people than Hedda herself. In her efforts to play the game and rid herself of Brack's threats, Hedda destroys Lovborg: the absence of Lovborg means that Brack can no longer hold the threat of ruining Hedda's reputation over her head.
In the fourth act, all of these threads in this drawing-room reenactment of life converge in a final struggle for power and control. Hedda has essentially commanded Lovborg to his grave; Brack will be left without his prime source of control over Hedda; Mrs. Elvsted has lost her love; Tesman will return to find that the manuscript he entrusted to his wife has seemingly evaporated. Hedda is very much the ringmaster at the end of the fourth act, but can she maintain this level of control, or will her need for power be her undoing?