Farnham is a self-made man who sees nuclear war coming and who builds a shelter under his house; only to find it thrust into a strange universe when the bomb explodes. In this future world all civilization in the northern hemisphere has long been destroyed, and Farnham and his family are fit to be slaves under the new regime.
A classic Heinlein, take one 1950's leave it to beaver family of four, a dinner guest and the kitchen help, add an atomic war and a well stocked bomb shelter. Shake well and displace a thousand years into the future. Good stuff. A bit odd at times but thats what you get when you stir in social commentary with a good survival/adventure/apocalypse theme.