It is early morning when the train reaches Milan and after an ambulance ride to the new hospital, Frederic is painfully carried into the elevator. He is the hospital's first patient. The elderly nurse and the attendants, who are roused from sleep, insist that they are not ready for a patient, but the pain in Frederic's legs compels him to insist that he be put into a room immediately. He is placed on an unmade bed in a room that smells of new furniture. After tipping the men that carried him up, he gives his papers to the nurse but she cannot read Italian and begins to cry. He learns that her name is Mrs. Walker and in a kindly tone he tells her and the porter to leave so that he can sleep.
When he wakes, a young pretty nurse is there. He asks if Miss Barkley has arrived but learns that she has not. The younger nurse, whose name is Miss Gage, washes him and tells him that the doctor is away but will return. He jokes with Miss Gage about his wounds. She and Mrs. Walker change the bed while he is still lying on it, a process he describes as an "admirable proceeding." He learns that at the moment there are just two nurses plus Miss Van Campen the superintendent. Miss Gage doesn't know when the new nurses will be arriving. That afternoon the stuffy and proper Miss Van Campen pays him a visit and they immediately take a dislike to one another. She forbids him to have any wine. After she leaves, however, he sends the porter out for two bottles and drinks one of them while he reads the papers. Miss Gage returns with some eggnog and sherry and later some supper. After eating, Frederic falls asleep for the night, awaking once from a bad dream and then again at dawn before falling back to sleep.
Miss Gage comes to bathe him. She tells him that she found his bottle of vermouth while he was sleeping and that she has placed both bottles in the room's amoire. She admonishes him for not asking for a glass and sharing the bottle with her. She tells him that Miss Barkley has arrived and Frederic requests a barber. The barber acts very suspiciously and afterward the amused porter tells him that the barber thought Frederic was an Austrian officer. Catherine comes to see him and he suddenly realizes that he is in love with her. He convinces her to have intercourse and afterward she cautions that they must be very careful not to be discovered. After she leaves, he admits to himself that he had not want to fall in love with her but since it has happened he is happy. Later Miss Gage tells him that the doctor will be there that afternoon.
The doctor, a thin and quiet man, probes Frederic's wounds and removes several small steel splinters. He sends Frederic to another hospital for x-rays and later Catherine comes to the room to show them to Frederic. After a while, three doctors arrive. Frederic observes that they do not seem to be very competent and he rejects their assessment that they must wait at least six months before they can remove the shrapnel. After they leave, Frederic asks the house doctor to return and explains that he cannot wait six months. The house doctor mistakes his impatience as an honorable desire to return to the fighting. The house doctor agrees to send another surgeon and refuses a drink before he leaves. The new doctor, Doctor Valentini arrives in much haste. He immediately gleans that Catherine and Frederic are lovers and makes much merriment out of the situation. When Frederic offers him a drink, he readily accepts. Dr. Valentini states that he will operate in the morning and promises to bring better cognac. Frederic notes that unlike the other doctor, who was a captain, this doctor is a major.
Catherine surreptitiously spends the night before the operation with Frederic. The next morning, while she prepares him for surgery, they banter about their relationship and she asks him not to think of her when he goes under the ether or he might talk too much. She questions him about his past lovers and they humor each other with the lie that he has never been with anyone but her. She promises to be dutiful to him always. He convinces her to return to bed with him and she readily capitulates.
When Frederic wakes up after the operation, he is very nauseous. Miss Gage tells him that the doctor did a good job on his knee. Some time passes and other patients arrive at the hospital. Catherine becomes popular among the nurses because she is always willing to do night duty. During a conversation with Miss Ferguson, who aids their relationship by passing notes between them during the day, Frederic asks if she will come to their wedding and she declares that they will quarrel or he will die before they marry. She warns him not to get Catherine in trouble and leave her with a war baby and he promises he that he will not. Miss Ferguson implores Frederic to ask Catherine to stay off night duty for awhile because she is getting tired and Miss Van Campen is growing suspicious. Later Frederic asks Miss Gage to advise Catherine to lay off night duty and she admits that she knows of their romance. She accepts a drink and advises Frederic that she is a true friend and one day he will appreciate it. Catherine is off night duty for three days and when she comes back it's as if they had been parted for much longer.
Frederic and Catherine have a wonderful summer while he recovers from the surgery. They go for carriage rides and become regulars at a restaurant where the headwaiter befriends them and even loans Frederic some money when he is short. In the evenings they frequent the shops and then in the nights they sit on the balcony outside his room. Later, after Catherine determines it is safe, they go to bed together and he explores her body. Each of them considers themselves married but Catherine points out that if they had an actual ceremony, rules would require that she be sent away soon afterward. Frederic wants to be really married and worries about a baby, but Catherine insists that they are as good as married already. She confesses that she can't bear to be separated from him and she will always be faithful. He comments that soon he will have to return to the front and she begs him to think instead about their present joy.
In a series of passages, Frederic describes to the reader some of the more pleasurable events during the summer of his convalescence. Thanks to the physical therapy, his leg heals quickly. The Italians have many victories in the war and Milan is a joyful place. He walks with a cane and sometimes goes to the races or the cafes and at other times he goes to the Anglo-American Club to read magazines. Because he is no longer on crutches, he and Catherine's outings must now be chaperoned. Miss Van Campen accepts that Catherine and Frederic have a blossoming relationship. Frederic notes that though the United States enters the war that summer, it will take a year to get any sizable force of troops trained and over the Atlantic. Since things are going poorly in France, he thinks that the war might go on for quite some time. He notes that the Italians are losing too many men in their battles and observes that Napoleon would have let his enemy come to him instead of making risky attacks in the mountains.
Frederic describes meeting "old Meyers and his wife" one afternoon. They discuss the races and Mrs. Meyers tells Frederic that he and all the other wounded at the hospital are her "dear boys." After seeing the Meyers, Frederic buys some chocolates for Catherine and stops to have a drink with some people he knows, a vice-counsel, two men studying singing and Ettore Moretti, an Italian from San Francisco serving in the Italian army. One of the singers is named Ralph Simmons but is singing under the name Enrico DelCredo and the other is named Edgar Suanders and sings under the pseudonym of Edourado Giovanni. The trio poke fun at each other about their abilities and the difficulty of performing in certain Italian cities. Ettore has many medals and congratulates Frederic on the silver medal they all believe he will receive. Ettore shows off his scars and advises Frederic to enlist in the American army so he will make more money. Frederic notes that Ettore was a genuine hero who bored everyone he met and Catherine could not stand him.
Later, on the balcony, Catherine says she only wants Frederic to have enough rank to get into the better restaurants and when he admits that he already holds that rank, she says it is a "splendid rank." It's raining as they talk on the balcony and Catherine confesses that she has always been afraid of the rain. Frederic says that he likes the rain but that he loves her. She admits that she fears the rain because sometimes she can envision herself or him dead in it. She begins to cry and he comforts her.
Throughout the novel Frederic Henry's outlook on life remains that of a Hemingway hero (i.e. Jake Barnes in The Sun Also Rises and Robert Jordan in For Whom the Bell Tolls). These men are somewhat detached from life but vigorously engaged in living with little patience for those who disagree. For instance, those doctors who want to wait to operate are portrayed as timid and fearful. They don't drink and have low rank. Dr. Valentini, on the other hand, wants to operate immediately, readily accepts a drink, has the insight to see Catherine and Frederic's love and holds the rank of major. He is the embodiment of the self-assured man and it is by this gauging rather than nervously proffered medical advice that Frederic basis his opinion.
During this part of the story Frederic and Catherine fall in love and their romance develops both emotionally and physically. They are both now admittedly in love with one another and consummate that love in Frederic's hospital bed. The war recedes into the background and we glimpse it only as the headlines in the papers that Frederic reads or in the mood of the people of Milan. The scenes during which Frederic and Catherine interact with people outside their relationship, people like the Meyers or Frederic's singing friends, add color to the story and serve to remind the reader that Frederic and Catherine increasingly view themselves and their love as apart from the real world. Of course, both Frederic and Catherine know that their summer idyll must come to an end. Catherine's confession that the rain causes her to think of death reveals that she at least is coming to terms with the uncertainties looming in their future.