Pierre and Jean is not the novel Maupassant writes about in his famous introductory essay, 'The Novel.' Indeed, the essay is more famous than the novel that follows. The essay is Maupassant's only critical work, whereas he wrote hundreds of short stories and five or six novels in his single full decade as an author. In it he explains why the psychological novel is bound to fail - because the only psychology we are really familiar with is our own. He then gives us, in Pierre and Jean, a psychological novel.
It is primarily the psychology of Pierre which dominates. The Roland brothers of Le Havre are unusually fraternal. Pierre has qualified as a doctor, Jean a lawyer; both are living with their parents while they lay the foundations for a career. Both are enamoured with the pretty widow Madame Rosemilly and maintain an amicable rivalry.
Then, out of the blue, an old family friend bequeathes his fortune to the younger brother, Jean. Pierre is initially happy for his brother. Then the questions start in his head. Why Jean, not him? Why not half each? Questions become suspicions. Suspicions fester, poisoning Pierre's relationship with his brother and, especially, their mother.
Maupassant is a naturalisr. He knows that in the real world these things result in compromise, not tragedy. Arrangements are made, an outcome acceptable to all parties is negotiated. And so it is here. The lives of all four main characters are changed but not ruined. The door to rapproachment is left open.
And it is beautifully done, the work of a master at the height of his powers. It is not really a novel, of course, only 130 pages. But every page is packed with life and detail, to a much greater extent than a short story. The cast is small, four principals and three or four bit-part-players, all expertly characterised, the action continuous and compressed. It's the perfect novella.