In the first part the narrator is sleeping with his girlfriend, who happens to be called Marie, when he receives a phone call from the Marie of the title, the same Marie (er, yes, but...) as we have met in the other books. She has been with the man the narrator has called Jean-Christophe de G. in Nue, whom he's been secretly watching at Contemporary Art Space in Tokyo, only that doesn't seem to be his real name but it who's splitting hairs: he's died of a heart attack in Marie's room anyway.
The second part goes back in time to when Marie is leaving Tokyo with Jean-Christophe de G., who has asked her to go with him when he returns his horse Zahir. Here we learn a great deal – probably far too much – about taking horses onto planes. Zahir escapes near the plane and has to be coaxed into returning and still causes a fuss on the plane anyway. He also vomits, which of course horses don't do, but that's not the point. And interestingly enough, the narrator later sees Marie with Jean-Christophe de G. and tells us that he doesn't know him: well, different book.
In the final section, Marie, has been staying on Elba in her father's house following his death a year before – which would be baffling if the reader thought about it too much, but that of course is not the thing to do. And we hardly learn anything of Maurizio, who is supposed to be guarding the house, but anyway didn't he die? Oh, wrong book, different story. I really must read this series again some time, as Jean-Philippe seems to be one of the most fascinating writers in the French language. But then, have I ever come across a writer in the Minuit stable whom I've not liked? Rhetorical question.
My other posts on Jean-Philippe Toussaint:
Jean-Philippe Toussaint: Fuir | Running Away
Jean-Philippe Toussaint: Faire l'amour | Making Love
Jean-Philippe Toussaint: Nue