It's a collection of dodgy old jokes based around the Irish-are-thick stereotype. There's no plot to speak of, no coherence or structure to be found apart from the arbitrary slicing of the prose into chapters. It reads like a stream of consciousness experiment rather than a novel. It wouldn't be so bad if the jokes were funny, but they are not.
I guess even geniusseses have off days. Steer clear of this book, read the war memoirs instead.