Edward and Lavinia Chamberlayne are separated after five years of marriage. She leaves Edward just as they are about to host a cocktail party at their London home, and he has to come up with an explanation for why Lavinia is not present, in order to keep up social appearances. Lavinia is brought back by a mysterious Unidentified Guest at the party, who turns out to be a psychologist whom Edward and Lavinia both consult. They each learn that they have been deceiving themselves and must face life's realities.
They learn that their life together, though hollow and superficial, is preferable to life apart. This message is difficult for the play's third main character, Edward's mistress, to accept. She, with the psychiatrist's urging, also moves on towards a life of greater honesty and salvation and becomes a Christian martyr in Africa. Two years later, Edward and Lavinia, now better adjusted, host another cocktail party.