Billy Prior is determined to re-enter the war in the late summer of 1918, anxious to take part in what is dubbed the "final push", a ferocious military campaign design to justify the slaughter and loss of life that has gone on for the past four years, and believed to guarantee a victory. Dr Rivers, the famed psychiatrist at Craiglockhart Military Hospital, who has treated Prior for shell-shock, is opposed to him going back, but Prior passes his physical and is approved by the medical board whose main concern was his asthma, leaving his shell-shock unacknowledged as they simply do not choose to believe in it as a mental illness. Before he returns to France, alongside fellow Craiglockhart alumnus Wilfred Owen, he visits his fiancé for the weekend, although they struggle to find any private time for themselves as Sarah's mother, Ada Lumb, is determined not to leave them alone for a minute. Nonetheless they do manage to sneak in some time whilst Ada is at a seance, and when the condom they are using breaks, Prior is worried that Sarah will fall pregnant; weeks later when he hears from her that she is not, he is strangely disappointed. Prior begins keeping a journal for his fourth time in France. He is seen off at the station by Charles Manning, a retired officer with whom he is having an affair. Manning is also opposed to him returning to the war and has even managed to find him a desk job in the war office in London but Prior turns him down.
The men going to France are a mixture of seasoned returners like Prior, and first-timers barely out of high school. Prior's bunk mate, Hallett, falls into the latter category and is only a couple of months shy of missing the war altogether because he is almost too young to be called up; a lack of surviving soldiers has made the minimum age requirement for going to join the war significantly more flexible. Prior, Hallet and Owen are posted two the 2nd Manchesters regiment and for a time he and the men under his command set up camp in a town that had been bombed out as the English army pushed the Germans back. Occasionally the wounded are rushed through the street, making the new recruits fear for their own mortality and reminding Prior that men like himself and Owen are depressingly immune to the sight. Shortly, Prior chooses his servant, a right that he has as regimental officer, selecting a man called Longstaffe who used to be an actor and whose over-dramatic performances at bayonet practice have made him stand out. It transpires that the 2nd Manchesters have had a bad time and suffered many losses. They come back to the town to join the new influx, and Prior recognizes Marshall of the Ten Wounds, a seemingly indestructible officer with a chest full of medals. Their last night in Amiens is stormy.
They set up camp in abandoned German trenches. Longstaffe is killed by German fire; stretcher bearers go into No Mans Land and are killed. They hear a horrible gutteral gurgling which they find to be Hallett who's head has been half blown away yet he does not die; he is sent home and hospitalized at Craiglockhart with Dr Rivers. Prior is recommended for the high honor of Military Cross for going out to bring Hallet in. Orders come that there is to be no talk of peace among the men but they are all aware that negotiations are going on to end the war and for England to declare defeat. Despite this the men are still sent into situations that will almost certainly kill them. They are also exhausted from long, arduous marching from one town to the next. They arrive in another village and set up camp as the Germans are dug in on the other side of the Sambre-Oise Canal and are ready to make a stand. The 2nd Manchesters are on a hiding to nothing; if they heavily bombard the Germans the rain soaked ditches will burst and the field will be impassable. If they lightly attack and move it onwards quickly they will leave too many of the German infantry alive and become sitting ducks themselves; however the latter is the plan chosen.
Meanwhile back in England, Rivers is suffering from Spanish influenza and is delirious and hallucinating about his time spent with the head hunters of the South Pacific Islanders and finding correlation between their culture of death and the men returning as shells of men from France. He treats a man who hears voices telling him he let his men down and he treats Hallet, sitting with his family as Hallet does slowly, his lady unintelligible words telling them "it's not worth it".
Prior and his men advance towards the German positions as they are systematically picked off; Prior sees Owen killed, then is hit himself. Unable to move he is hit a second time and dies shortly before the war ends on a cold November day by the Sambre-Oise Canal.
