A 78-year-old man hides in a wardrobe, peeping at a young couple having sex in a hotel bedroom. The man is Haffner, a secular Jew and retired banker, who is in Switzerland to recover a villa confiscated from his family by the Nazis. As well as his peeping activities, he also finds time to have an affair with a middle-aged German woman; and his grandson comes to visit.
The novel meanders back and forth in time, revisiting Haffner's marriage, his old friends, and his service during the war. The writing is polished and full of allusions. Then there are the epigrams, some of which work ("To be bohemian you had to be an absolute insider") and some of which don't ("For how can a man be young when he is old?").
You could look at any individual page of this and think, "That's good; that's clever." But taken as a whole, it's insubstantial. It just doesn't feel like a proper novel to me.