The narrator again expresses his view that war is not scientific, repeating that the French defeat in Russia is rationally unexplainable. He then describes the devastation of the remaining French troops by Russian guerillas.
Dolokhov and Denisov are among the Cossack partisan fighters tracking the retreating French. Denisov receives a message delivered by Petya Rostov, who is now proudly serving in the army. Denisov and Petya come upon a French encampment and consider attacking it. Suddenly, they see a Russian peasant fleeing the French camp, whom Denisov recognizes as Tikhon, a feisty character who enjoys looting the French soldiers. Tikhon is sent off to capture a French informer, but kills the first Frenchman he finds on grounds that his clothes are not fancy enough. Denisov is disgusted by Tikhon’s cruelty. Petya, eager to please Denisov, acts kindly toward a French drummer boy the Russians have taken prisoner. Petya hopes to take part in the attack on the French camp planned for the next day, and is finally allowed to do so.
Dolokhov and Petya, disguised as French officers, enter the French camp for information about Russian prisoners of war. Back at the Russian guerilla camp, Petya is unable to sleep before the -battle, so he goes out to speak to a Cossack who sharpens Petya’s saber. Petya feels as though he is in a dream. When the battle begins, the overjoyed Petya rides with glee into the heart of the shooting. He is killed.
Entering the French camp, Dolokhov and Denisov liberate the Russian prisoners of war, including Pierre, who had been marching painfully with the French while his friend Platon Karataev grew more and more ill. One day, Platon had told a tale of a merchant who suffered for the sins of others and greeted death happily. The next day, the French had shot Platon for being ill and straggling behind the rest. When Dolokhov and Denisov release Pierre, he weeps with joy. Petya is buried.
The French army continues to disintegrate. The troops fight among themselves and plunder each other. Napoleon abandons his subordinates. Nevertheless, Russians readers of histories of the war are frustrated to note that the Russian forces were unable to destroy the remnants of the French army. The narrator explains that attacking the retreating French would have been senseless, like whipping an animal already running.
Mary and Natasha, still in exile from Moscow, grieve Andrew’s death in silence and pain. Natasha is much changed, and she refuses to return to Moscow even when the danger is past. She receives word that her brother Petya is dead, and tells her mother, both weeping. Mary attempts to console Natasha, who grows so pale and thin that her father insists that she accompany Mary to Moscow to see doctors.