Catholic clergy who run the school attended by Jacques Thibault have discovered a grey notebook containing messages between him and a Protestant fellow schoolboy, Daniel de Fontanin.
Jacques's widowed father Oscar Thibault, a stern Catholic with a position in society, dispatches his older son, Antoine, a medical student, to look for them.
Daniel's younger sister Jenny falls seriously ill and Thérèse, their mother, goes looking for her errant husband Jérôme, to discover that his list of conquests now includes her cousin Noémie.
Antoine visits the de Fontanin apartment and regretfully concludes that Jenny is beyond medical help, but the girl recovers after the intervention of James, a Christian Science faith healer.
Jenny finds herself increasingly conflicted about her feelings towards Jacques, and when her mother returns from Holland, with Jérôme in tow, she breaks down sobbing, though she can't bring herself to fully confess her emotions.
Rachel tells Antoine about the dark chapters in her past, including the suicide of her brother and the death of her infant daughter, and reveals her relationship to a sinister man named Hirsch.
Much of the narrative centers on Antoine's patients; one of these, a gravely ill infant, is the daughter of Daniel's cousin Nicole, who is now married to a physician named Héquet.
His ailing father believes that he has committed suicide, but Antoine discovers that someone using the name "Jack Baulthy" has recently published a novella in a Swiss magazine and quickly determines that the author is his brother.
Written in a florid style and set in Italy, the novella, which itself is entitled La sorellina ("The Little Sister" in Italian), proves to be a roman à clef.
Its hero, Giuseppe, has defied his devoutly Catholic father and fallen in love with a young English Protestant named Sybil (based on Jenny); but he has also developed an ardent—and reciprocated—attraction for his younger sister Annetta, a character clearly modeled on Gise.
With Oscar dead, Antoine goes through his father's papers and effects and finds some photographs and letters that suggest that he may secretly have developed a sentimental attachment of some kind to another woman in the years after his wife's death.
Jacques doesn't attend the funeral but makes a trip on his own to visit his father's grave; an unidentified older woman leaves flowers there at the same time.
7. l'Été 1914 ("Summer 1914"), the longest of the eight volumes, is set in the period leading up to and including the beginning of World War I. Antoine Thibault is now a well-to-do physician who is having an affair with a married woman, Anne de Battaincourt; his brother Jacques, on the other hand, is a committed socialist who spends much of his time among radical political circles in Geneva.
Daniel de Fontanin, by now a promising painter, is continuing his military service, but is called home when his father, Jérôme, commits suicide after being accused of embezzlement.
While she is absent, Jacques and Jenny de Fontanin, overcoming their apparent longstanding antipathy to each other, become lovers, and while dining together witness the assassination of the antiwar socialist leader Jean Jaurès by a French nationalist.
Disgusted by the failure of the Left to stop the war, Jacques, who refuses to fight under any circumstances, escapes to Switzerland with false papers, while Jenny remains in Paris, intending to join him later.
After the plane crashes, killing Meynestrel, Jacques, gravely injured, is seized as a spy by French soldiers and is summarily executed as the overwhelmed troops beat a hasty retreat.
The novel was admired by André Gide, a longtime friend, and by Albert Camus,[3] Clifton Fadiman,[4] and Georg Lukacs,[5] but Mary McCarthy called it "a work whose learned obtuseness is, so far as I know, unequaled in fiction.