Misalliance is an ironic examination of the mating instincts of a varied group of people gathered at a wealthy man's country home on a summer weekend. Most of the romantic interest centers on the host's daughter, Hypatia Tarleton, a typical Shaw heroine who exemplifies his lifelong theory that in courtship, women are the relentless pursuers and men the apprehensively pursued.

Hypatia is the daughter of newly-wealthy John Tarleton who made his fortune in the unglamorous but lucrative underwear business. She is fed up with the stuffy conventions that surround her and with the hyperactive talk of the men in her life. Hypatia is engaged to Bentley Summerhays, an intellectually bright but physically and emotionally underdeveloped aristocrat.

Hypatia is restless with her engagement as the play starts, even as it is revealed she has also had a proposal of engagement from her betrothed's father, Lord Summerhays. She has no desire to be a nurse to the elderly and is in no hurry to be made a widow. She longs for some adventure to drop out of the sky, and it does ... an aircraft crashes through the roof of the conservatory to close the end of the first act.

At the beginning of Act II, it is revealed that the aircraft brings two unexpected guests. The pilot, Joey Percival, is a handsome young man who immediately arouses Hypatia's hunting instinct. The passenger, Lina Szczepanowska, is a female dare-devil of a circus acrobat whose vitality and directness inflame all the other men at the house-party.

An additional uninvited guest arrives in the form of Gunner. He is a cashier who is very unhappy with his lot in life. He blames the wealthy class in particular for the plight of the ordinary worker, and he blames John Tarleton in particular for a romantic dalliance that he once had with Gunner's mother. Gunner arrives with intent to kill Tarleton but hides inside a piece of furniture. From this position, he becomes wise to Hypatia's pursuit of Percival. His character comes to introduce the themes of socialism to the play, as well as serving to question the conventional views on marriage and social order.

All together there are eight marriage proposals offered for consideration in the course of one summer afternoon.