Act I
Act one is an amalgam of early 20th century New Jersey and the dawn of the Ice Age. The father is inventing things such as the lever, the wheel, the alphabet, and multiplication tables. The family (the Antrobuses) and the entire north-eastern U.S. face extinction by a wall of ice moving southward from Canada. The story is introduced by a narrator and further expanded by the family maid, Sabina. There are unsettling parallels between the members of the Antrobus family and various characters from the Bible. In addition, time is compressed and scrambled to such an extent that the refugees who arrive at the Antrobus house seeking food and fire include the Old Testament judge Moses, the ancient Greek poet Homer, and women who are identified as Muses.
Act II
Act II takes place on the Boardwalk at Atlantic City, New Jersey, where the Antrobuses are present for George's swearing-in as president of the Ancient and Honorable Order of Mammals, Subdivision Humans. Sabina is present, also, in the guise of a scheming beauty queen, who tries to steal George's affection from his wife and family. Although the conventioneers are rowdy and partying furiously, there is an undercurrent of foreboding, since the weather signals change from summery sunshine to hurricane to deluge. (A fortune teller had previously attempted to warn them about this but had been ignored). Gladys and George each attempt their individual rebellions, and are brought back into line by the family. The act ends with the family members reconciled and, paralleling the Bibilical story of Noah's Ark, directing pairs of animals to safety on a large boat where they survive the storm and/or the end of the world.
Act III
The final act takes place in the ruins of the Antrobuses' former home. A devastating war has occurred; Maggie and Gladys have survived by hiding in a cellar. When they come out of the cellar we see that Gladys has a baby. Sabina joins them, "dressed as a Napoleonic camp-follower". George has been away at the front lines leading an army. Henry also fought, on the opposite side, and returns as a general. The family members discuss the ability of the human race to rebuild and continue after continually destroying itself. The question is raised, 'is there any accomplishment or attribute of the human race of enough value that its civilization should be rebuilt'?
The stage manager interrupts the play-within-the-play to explain that several members of their company can't do their parts because they're sick (possibly with food poisoning: the actress playing Sabina claims she saw blue mold on the lemon meringue pie at dinner). The stage manager drafts a janitor, a dresser, and other non-actors to fill their parts, which involve quoting philosophers such as Plato and Aristotle to mark the passing of time within the play.
The alternate history action ends where it began, with Sabina dusting the living room and worrying about George's arrival from the office. Her final act is to address the audience and turn over the responsibility of continuing the action, or life, to them.
