The (anti-)hero of the work is the narrator Sébastien Perrin, who's a thirty-year-old history teacher at a school in a well-heeled area of Paris and married to Sophie. They live in a block of flats which also houses a general and a viscount, and life is very monotonous for Sébastien, who decides to liven things up by not only changing the history syllabus but changing history itself, at least from the way he teaches it. One of the important changes he makes is not to include the signing of the Treaty of Westphalia, which would also change many other things. As an example of the thinking, when Sophie and Sébastien are celebrating their fifth wedding anniversary, the waiter whispers that there's no more Alsace, whereupon Sébastien looks at Sophie and declares that it's started: what Sébastien jokes has started is the messing up of history – the waiter is of course talking about wine, whereas Sébastien's talking geographical change.
During the Nazi occupation Sébastien was, like many other French workers, forced to do his STO (Service du travail obligatoire) in Germany, and on the way back home he worked as a groom and became amorously involved with Princess Albertina of Arunsberg-Giessen, although back in France he ended the relationship by informing her (ostensibly via a third party) that he had died.
However, Albertina later goes to France with her uncle and meets the 'dead' man, and of course they have a secret affair and she gets pregnant. Or at least so she thinks. I very rarely give up on reading a book, and although in the early stages I was slightly tempted to abandon this in the same way that I know others have done, I'm glad I stuck with it: the humour grows on you.