This selection of chapters opens with the details of an afternoon at the races. In addition to Frederic and Catherine, the party includes Miss Ferguson and a fellow patient at the hospital named Crowell Rodgers who has been wounded in the eyes. Frederic notes that the racing in Italy was crooked and only the most disreputable jockeys were racing there. Old Meyers always has inside information and occasionally gives Frederic or more often Rodgers a tip. Mr. Meyers never gives his wife any information. Mrs. Meyers talks constantly. The party bets on a horse called Japalac that looks like it has been dyed. Sure enough, the horse is a ringer and despite the jockey's efforts to reign him in, Japalac finishes well ahead of the others. Catherine is disappointed when Meyers tells her that instead of paying thirty five-to-one, the horse will barely pay two-to-one because of last minute betting. At the betting booths they have whiskey and soda and old Meyers gives them a tip on a horse that wins but due to crooked betting doesn't pay anything. Catherine and Frederic leave the party to get nearer the horses and bet on a loser that makes Catherine happy. They admit to each other that they like being alone together more than with the group. They are happy.
September comes and the nights turn cold. The racing has moved back to Rome and the war is going badly for the Italians who cannot take the well-fortified mountain town of San Gabriel. There are riots against the war and the Italian army continues to lose many men. Frederic meets a pessimistic British major who declares that the Italians have bitten off more than they can chew and the whole war is going very badly. On the way home, an old man cuts Frederic's silhouette and does not charge him for the work. At the hospital there is mail, including a letter that says that he must return to service three weeks after his treatment is finished - the date he must return is October twenty-fifth. One of the letters is from Rinaldi who wants some phonograph records. Frederic goes to bed and reads the American papers, which are all about baseball and training camps, and he is glad he is not in a training camp. Catherine comes at 9 o'clock and they discuss where they will go during his three weeks of leave. She seems upset and after he questions her several times she admits that she is three month's pregnant. She admonishes him not to worry on her behalf and that she will see to everything. After an awkward moment, they agree to be one soul again and not let anything come between them. They discuss the nature of bravery and she pours him a drink. She leaves to look after the other patients but agrees to return.
The weather turns cold and rainy and Frederic contracts jaundice which prevents him and Catherine from going anywhere during his three weeks of leave. While he is convalescing Miss Van Campen finds the empty bottles of brandy in the amoire and accuses Frederic of intentionally contracting jaundice with alcoholism in order to avoid being sent to the front. He counters by asking how many of her patients have avoided the front by kicking themselves in the scrotum - the nearest sensation to jaundice he can conjure and one he doesn't believe that a woman can appreciate. Miss Van Campen leaves in a huff but Miss Gage comes later and admonishes Frederic for not having disposed of the bottles earlier. Miss Van Campen takes the bottles and makes a report of Frederic's drinking, but nothing happens as a result.
The night, Frederic must leave to return to the front and he sends the porter with his luggage to hold a place on the train. He spends some time in a cafe drinking coffee and grappa before he meets Catherine and they walk toward the station. They stop at an armorer's shop and Frederic purchases a new pistol that fits his holster. They walk a bit further and kiss. Catherine agrees to accompany Frederic to a hotel across from the train station but protests that she doesn't have a nightgown. They hail a carriage and stop at a shop where she purchases a nightgown. They go to the hotel and order dinner for the room. The room is lavishly but cheaply furnished with velvet and mirrors. Catherine is unhappy and admits that she feels like a whore. She recovers her spirits quickly, however, and they eat and then make love and feel much better. The room begins to seem much more like their own and they get drunk together. Catherine promises to write every day Frederic is at the front and they discuss the happy life they will lead when he has returned.
It is raining. Frederic and Catherine get a carriage and she leaves him at the station with few words. On the train, Frederic takes the place saved by the porter's friend but a captain accosts him and insists that he has no right to have a seat saved. After a moment's hesitation, Frederic gives the captain the seat and tips the porter and his friend. Frederic knows he has no chance of a seat for most of the trip. Frederic sleeps on the floor of the train.
This latter portion of Book 3 concludes the idyll in Milan. As the weather turns from summer to fall the lover's humor begins to change as well. Lighthearted episodes like the day at the races, during which Catherine and Frederic fully realize their complete happiness with one another, are replaced with more serious moments such as the pessimistic British officer's morose assessment of the war. Most significantly, Catherine admits that she is pregnant and the couple experiences their first misunderstanding and feeling of distance. Though they reaffirm their love, the coming child and looming separation means that they will face great obstacles. Finally, as the time for Federic's departure grows near, the couple's luck begins to turn for the worse. He develops jaundice and spends his leave time recovering. The rain that permeates their parting sets a somber mood and recalls Catherine's fear of death.