Frederic Henry is an American serving as a Lieutenant of an ambulance division in the Italian Army. In the first part of the book, Fred goes on leave to Naples and returns. Through his friend, Lt. Rinaldi, he meets a British nurses' aide named Catherine Barkley whose fiancee perished the previous year in the Somme. Fred is immediately smitten with Catherine and he spends a lot of time courting her. At the mess hall, they make fun of Fred's other friend, the priest. As the snows clear, it is time for the offensive to begin again, and Fred goes with his three ambulances to a post in the mountains. During the first night here, there is a bombardment and Fred is seriously wounded in the legs. One of his drivers is also wounded and another is killed. Fred is shipped to a field hospital, but when an American hospital is opened in Milan, he is shipped there.
Fred is not expected by the hospital in Milan, but they receive him anyway. Catherine comes with her friend, Miss Ferguson, to work at this hospital and be close to him. The first estimate for Fred's recovery is six months, but a second doctor operates on him almost immediately. Before long, Fred is walking on crutches and going to restaurants with Catherine. She works the night shift so they can be together at night. Fred has begun to drink too much. Once recovered, Fred is granted a threeweek leave but he loses it because he comes down with jaundice from drinking too much. Catherine confesses to him that she has become pregnant; Fred is not upset with her, only worried. Before he is to return to the front, they spend a night together in a hotel. He leaves on a train in the middle of the night to return to Gorizia.
There are fewer people at Gorizia and the town is not as cheerful. Lt. Rinaldi has become more depressed. He makes a scene in the mess hall and then leaves. The priest and Fred talk about life and war. The next day Fred reports to a mountain post to find his ambulance team. That night there is an Austrian attack and they are forced to retreat.. After a couple of days, a traffic jam is created from all the people retreating. Fred directs his three trucks to take a side road. Soon after, the trucks become stuck. They must continue on foot. At a river, one of the drivers is killed. Soon after, another tries to leave, but is captured. After a day, Fred and his last driver attempt to rejoin the Italian army. The Italian officers, afraid of German spies, are interrogating and shooting anyone who is not Italian. Fred jumps into a river to escape execution,and floats for some time. He jumps a train and rides it to Milan.
In Milan, he finds out that Catherine has gone to a town called Stresa near the Swiss border. He gets some new clothing from a friend and takes a train to Stresa. He checks into a hotel and finds Catherine with her friend Miss Ferguson. They are happy to be reunited. However, Miss Ferguson isn't happy to see Fred because she doesn't trust him. They stay in Stresa for a day, but one night the bartender, who is Fred's friend, warns him that he is to be arrested in the morning. He offers them his boat to row to Switzerland. Fred rows through the night and arrives in Switzerland where he and Catherine are first arrested, but later issued provisional visas.
Together, Catherine and Fred stay in a remote mountain town called Montreux. They spend all of their time together reading, hiking, and talking. Catherine's pregnancy has matured and when the spring comes they move into a larger town. When Catherine goes into labor, they rush to the hospital. Even though it is early in the morning when they arrive, Catherine still hasn't delivered the baby by noon. The doctor suggests a caesarian. The operation seems to go well, but Fred soon finds out that Catherine has hemorrhaged and that the child was born dead, choked by its own umbilical cord. Soon after this, Catherine dies from repeated hemorrhaging.
