Act 3. The Chamberlayne's drawing room, two years later, July. A buffet table arrives and Lavinia tells a caterer to bring in glasses. Edward comes in and they joke about the fact that Lavinia might run away at the last minute. Edward compliments Lavinia's dress and they talk about the fact that more people accepted their invitation than they thought would, because they thought some of their invitees would go to the Gunnings' party. Edward thinks that the best moment is the moment before a party, while Lavinia suggests that the best moment is the moment it is over.
Lavinia wants to go away to a remote house together. Suddenly, the doorbell rings and Julia and Alex enter. Alex goes straight to the kitchen, as Julia says she's arriving early because she is hungry and thirsty and knows that the Gunnings will not have adequate refreshments. She tells them she brought Alex, who enters and announces that he wanted to be a surprise. He tells them that he just returned from Kinkanja, an island in the East, staying with the governor and inspecting the local conditions and some "unrest amongst the natives" about the unruliness of the monkey population. The natives have split themselves into a group that remains loyal to indigenous customs, and a Christianized group that slaughters and eats the monkeys. This has ended with the indigenous population eating members of the Christianized population.
Just as Alex goes to tell them some news, Peter appears and tells them that he has just arrived from Los Angeles. He tells them he's working for Pan-Am-Eagle, which is a film company. He tells them he's making a film about English life, for which he wrote the script. Julia wants Peter to persuade his casting director to bring them all over, but Peter does not think this is possible. Suddenly, Reilly enters, and Julia introduces him to everyone.
Peter asks the group about Celia, since she always wanted to get into films, and he thinks he could get her an introduction. Alex reveals that Celia is dead, killed by residents of the island of Kinkanja whom she was trying to help as a missionary. He tells them that she was likely crucified on an anthill, fighting to save "a handful of plague-stricken natives/Who would have died anyway."
Peter bemoans the fact that he only began to think of Celia again as he started to find some success, but she's dead now. Lavinia lectures Peter about the fact that none of them ever really knew Celia, that she was just a surface for their projections. Julia reminds Peter that he must go to Boltwell, and he leaves. After Peter leaves, Lavinia confronts Reilly about the fact that he was neither surprised nor horrified by the news of Celia's death, but rather, he seemed satisfied.
Alex tells the group that the "natives" made a shrine for Celia. Reilly tells the group that when he first met Celia, he saw that it was her destiny to die. He says that she suffered more because she was more conscious than any of them. Edward feels guilty for the death, but Reilly insists he did nothing wrong and that Celia's life was "triumphant." Julia says that Celia made a choice to die by crucifixion, and that life is just choices. The Chamberlaynes, she suggests, have made a choice that ended in a cocktail party, and Alex leaves the room.
Lavinia does not want to have the party, and Alex enters with some champagne. They toast to Lavinia's aunt and drink. Immediately afterward, Julia, Reilly, and Alex announce they are going to the Gunnings' party. Left alone, Edward and Lavinia anticipate the party starting.
The final act begins with Lavinia and Edward apparently having fallen into a pleasant marital rhythm. As they prepare for a cocktail party together, Edward teases Lavinia about her disappearance two years earlier and they seem to be looking out for one another in anticipation of the party. Their marriage in the preceding acts was completely on the rocks, toxic and mutually disadvantageous, but now they seem to have come together to work through these difficulties gracefully. It is quite a contrast from the earlier scenes, which have an almost haunted and dark quality to them. The "drawing room comedy" that Eliot has been playing with as a genre throughout becomes more tonally straightforward in this scene.
The "cocktail party" of the title is an existential proposition as much as a literal plot device. As Edward and Lavinia discuss the impending party, one senses that they are not simply talking about the party itself, but about their respective relationships to society and the public itself. Edward believes that the moment before the party is the best moment, while Lavinia suggests that the best moment is after. In this, we can see that the characters cannot decide if they are looking forward to coming into contact with the public or if they would rather enjoy its afterglow. The cocktail party of the first act was a closed society of friends trapped in a strange social arrangement and a plot on behalf of Edward and Lavinia's spiritual growth. Now that Edward and Lavinia have chosen to be together, the promise of a party is a different affair, a symbol of their relationship to the world at large.
The Cocktail Party, a definitively English play, includes references to the English colonies in the East and their legacy of violence and unrest. In the third act, Alex has just returned from a fictional island, Kinkanja, where the natives have split into two groups, one that is Christianized, and the other that has remained loyal to traditional indigenous customs. These two groups are fighting, Alex tells them, and resorting to murder and cannibalism in the process. Christians are being killed by the indigenous populations for bringing a curse to the island. Just under the surface of the decadent and "civilized" world is the darker side of English colonialism and the unrest and violence it has created. Eliot's political perspective on colonialism remains unclear. He presents us instead with an account of the privileged English society that benefits from such colonial projects, and remains at a distance from them.
Celia is the play's victim of this violence, a white Christian martyr in the colonies. Alex soon reveals to the group that Celia was killed by the "heathen" natives, "crucified very near an ant-hill." Here Eliot stages a racist, colonial fantasy, the image of the white woman savior seeking to bring salvation and peace to an "uncivilized" nation and getting killed for it. The "spiritual awakening" that she longed for in the second act was in fact a colonial fantasy of white Christian martyrdom, a sacrifice and a representation of what theater theorist Mary F. Brewer describes as the "white burden" as written in English literature at the time. She wrote of Eliot's play, "Just as humanitarian aims were put forward as excuses for imperial expansion at the height of empire, British imperialists after the war masked their opposition to the transfer of colonial power by portraying British rule as a necessary, albeit unappreciated, system of benevolent caretaking. Opponents to nationalist movements warned that, bereft of British protection, the colonies would descend into chaos and return to the kind of 'darkness and death' that Eliot ascribes to the non-Christian people of Kinkanja."
The play begins with the characters resuming their normal lives, repressing the emotions that accompany their grief and confusion about Celia, and continuing on as normal. They give a lighthearted toast to Lavinia's aunt, and the circle of friends disperses. The final image is that of Edward and Lavinia, waiting for the party to begin. It is a curious ending to a play that climaxes with a revelation about the death of an English girl in the colonies, and it represents the British Empire's ability to continue reproducing itself, to continue drinking through the hard times and experience life from a detached remove.