It is the early 1960's and the cold war is getting chillier. An American family,led by Hugh Farnham, and complete with black servant, retreat to their bomb shelter just as the 3 minute warning sounds. To cut a long story short the bomb zaps them far into the future, where black rulers treat their white slaves like cattle. Don't tell me how far fetched it sounds - it is science fiction after all. The main thing is that here Heinlein is making the uneasy transition from juvenile fiction to adult stories with a whole heap of social comment and homespun philosophy. The story is a vehicle for Heinlein's confused politics - right wing frontiersman attitudes bound up with an appeal for racial equality, although the dating of the book form 1964 causes chuckles to be raised by the dialogue that seems patronising now, such as: 'Joe is not a nigger - he's a negro'. Heinlien always did like to challenge boundaries, as he did with cannabilism and homosexuality in Stranger in a Strange Land. It all seems fair enough now but probably raised eyebrows at the time. The trouble is, he didn't know where to stop. Taboos against mixed marriages and gays were rightly challenged as the result of blind socially conditioned prejudice, but in this and later works he starts on making incest acceptable, finally going all the way (so to speak) 25 years later in To Sail Beyond the Sunset, disregarding the sound biological basis for this taboo. Heinlein seems both obsessed and uncomfortable with sex of any kind, as FF demonstrates, as if he feels trapped in the juvenile fiction genre, but in spit of all this FF is a good read.