War and Peace has a large cast of characters, the majority of whom are introduced in the first book. Some are actual historical figures, such as Napoleon and Alexander I. While the scope of the novel is vast, it is centered around five aristocratic families. The plot and the interactions of the characters take place in the era surrounding the 1812 French invasion of Russia during the Napoleonic wars.
The novel begins in July 1805 in Saint Petersburg, at a soirée given by Anna Pavlovna Scherer—the maid of honour and confidante to the queen mother Maria Feodorovna. Many of the main characters and aristocratic families in the novel are introduced as they enter Anna Pavlovna's salon. Pierre (Pyotr Kirilovich) Bezukhov is the illegitimate son of a wealthy count, an elderly man who is dying after a series of strokes. Pierre is about to become embroiled in a struggle for his inheritance. Educated abroad at his father's expense following his mother's death, Pierre is essentially kindhearted, but socially awkward, and owing in part to his open, benevolent nature, finds it difficult to integrate into Petersburg society. It is known to everyone at the soirée that Pierre is his father's favorite of all the old count’s illegitimate children.
Also attending the soirée is Pierre's friend, the intelligent and sardonic Prince Andrei Nikolayevich Bolkonsky, husband of Lise, the charming society favourite. Finding Petersburg society unctuous and disillusioned with married life after discovering his wife is empty and superficial, Prince Andrei makes the fateful choice to be an aide-de-camp to Prince Mikhail Ilarionovich Kutuzov in the coming war against Napoleon.
The plot moves to Moscow, Russia's ancient city and former capital, contrasting its provincial, more Russian ways to the highly mannered society of Petersburg. The Rostov family are introduced. Count Ilya Andreyevich Rostov has four adolescent children. Thirteen-year-old Natasha (Natalia Ilyinichna) believes herself in love with Boris Drubetskoy, a disciplined young man who is about to join the army as an officer. Twenty-year-old Nikolai Ilyich pledges his love to Sonya (Sofia Alexandrovna), his fifteen-year-old cousin, an orphan who has been brought up by the Rostovs. The eldest child of the Rostov family, Vera Ilyinichna, is cold and somewhat haughty but has a good prospective marriage in a Russian-German officer, Adolf Karlovich Berg. Petya (Pyotr Ilyich) is nine and the youngest of the Rostov family; like his brother, he is impetuous and eager to join the army when of age. The heads of the family, Count Ilya Rostov and Countess Natalya Rostova, are an affectionate couple but forever worried about their disordered finances.
At Bald Hills, the Bolkonskys' country estate, Prince Andrei departs for war and leaves his terrified, pregnant wife Lise with his eccentric father Prince Nikolai Andreyevich Bolkonsky and devoutly religious sister Maria Nikolayevna Bolkonskaya, who refuses to marry the son of a wealthy aristocrat on account of her devotion to her father.
The second part opens with descriptions of the impending Russian-French war preparations. At the Schöngrabern engagement, Nikolai Rostov, who is now conscripted as ensign in a squadron of hussars, has his first taste of battle. Boris Drubetskoy introduces him to Prince Andrei, whom Rostov insults in a fit of impetuousness. Even more than most young soldiers, he is deeply attracted by Tsar Alexander's charisma. Nikolai gambles and socializes with his officer, Vasily Dmitrich Denisov, and befriends the ruthless, and perhaps, psychopathic Fyodor Ivanovich Dolokhov. Both Bolkonsky, Rostov and Denisov are involved in the disastrous Battle of Austerlitz, in which Andrei is wounded as he attempts to rescue a Russian standard.
Book Two begins with Nikolai Rostov briefly returning on home leave to Moscow. Nikolai finds the Rostov family facing financial ruin due to poor estate management. He spends an eventful winter at home, accompanied by his friend Denisov, his officer from the Pavlograd Regiment in which he serves. Natasha has blossomed into a beautiful young girl. Denisov falls in love with her, proposes marriage but is rejected. Although his mother pleads with Nikolai to find himself a good financial prospect in marriage, Nikolai refuses to accede to his mother's request. He promises to marry his childhood sweetheart, the dowry-less Sonya.
Pierre Bezukhov, upon finally receiving his massive inheritance, is suddenly transformed from a bumbling young man into the richest and most eligible bachelor in the Russian Empire. Despite rationally knowing that it is wrong, he is convinced into marriage with Prince Kuragin's beautiful and immoral daughter Hélène (Elena Vasilyevna Kuragina), to whom he is superficially attracted. Hélène, who is rumoured to be involved in an incestuous affair with her brother, the equally charming and immoral Anatol, tells Pierre that she will never have children with him. Hélène is rumoured to have an affair with Dolokhov, who mocks Pierre in public. Pierre loses his temper and challenges Dolokhov, a seasoned dueller and ruthless killer, to a duel. Unexpectedly, Pierre wounds Dolokhov. Hélène denies her affair, but Pierre is convinced of her guilt and, after almost being violent to her, leaves her. In his moral and spiritual confusion, Pierre joins the Freemasons, and becomes embroiled in Masonic internal politics. Much of Book Two concerns his struggles with his passions and his spiritual conflicts to be a better man. Now a rich aristocrat, he abandons his former carefree behavior and enters upon a philosophical quest particular to Tolstoy: how should one live a moral life in an ethically imperfect world? The question continually baffles Pierre. He attempts to liberate his serfs, but ultimately achieves nothing of note.
Pierre is vividly contrasted with the intelligent and ambitious Prince Andrei Bolkonsky. Andrei recovers from his near fatal artillery wound in a military hospital and returns home, only to find his wife Lise dying in childbirth. He is stricken by his guilty conscience for not treating Lise better when she was alive, and is haunted by the pitiful expression on his dead wife's face. His child, Nikolenka, survives.
Burdened with nihilistic disillusionment, Prince Andrei does not return to the army but chooses to remain on his estate, working on a project that would codify military behavior to solve problems of disorganization responsible for the loss of life on the Russian side. Pierre visits him and brings new questions: where is God in this amoral world? Pierre is interested in panentheism and the possibility of an afterlife.
Pierre's estranged wife, Hélène, begs him to take her back, and against his better judgment and in trying to abide by the Freemason laws of forgiveness, he does. Despite her vapid shallowness, Hélène establishes herself as an influential hostess in Petersburg society.
Prince Andrei feels impelled to take his newly written military notions to Petersburg, naively expecting to influence either the Emperor himself or those close to him. Young Natasha, also in Petersburg, is caught up in the excitement of dressing for her first grand ball, where she meets Prince Andrei and briefly reinvigorates him with her vivacious charm. Andrei believes he has found purpose in life again and, after paying the Rostovs several visits, proposes marriage to Natasha. However, old Prince Bolkonsky, Andrei's father, dislikes the Rostovs, opposes the marriage, and insists on a year's delay. Prince Andrei leaves to recuperate from his wounds abroad, leaving Natasha initially distraught. She soon recovers her spirits, however, and Count Rostov takes her and Sonya to spend some time with a friend in Moscow.
Natasha visits the Moscow opera, where she meets Hélène and her brother Anatole. Anatol has since married a Polish woman whom he has abandoned in Poland. He is very attracted to Natasha and is determined to seduce her. Hélène and Anatole conspire together to accomplish this plan. Anatole kisses Natasha and writes her passionate letters, eventually establishing plans to elope. Natasha is convinced that she loves Anatole and writes to Princess Maria, Andrei's sister, breaking off her engagement. At the last moment, Sonya discovers her plans to elope and foils them. Pierre is initially horrified by Natasha's behavior, but realizes he has fallen in love with her. During the time when the Great Comet of 1811–2 streaks the sky, life appears to begin anew for Pierre.
Prince Andrei coldly accepts Natasha's breaking of the engagement. He tells Pierre that his pride will not allow him to renew his proposal. Ashamed, Natasha makes a suicide attempt and is left seriously ill.
With the help of her family, especially Sonya, and the stirrings of religious faith, Natasha manages to persevere in Moscow through this dark period. Meanwhile, the whole of Russia is affected by the coming confrontation between Napoleon's troops and the Russian army. Pierre convinces himself through gematria that Napoleon is the Antichrist of the Book of Revelation. Old prince Bolkonsky dies of a stroke while trying to protect his estate from French marauders. No organized help from any Russian army seems available to the Bolkonskys, but Nikolai Rostov turns up at their estate in time to help put down an incipient peasant revolt. He finds himself attracted to Princess Maria, but remembers his promise to Sonya.
Back in Moscow, the war-obsessed Petya manages to snatch a loose piece of the Tsar's biscuit outside the Cathedral of the Assumption; he finally convinces his parents to allow him to enlist.
Napoleon himself is a main character in this section, and the novel presents him in vivid detail, as both a thinker and would-be strategist. His toilette and his customary attitudes and traits of mind are depicted in detail. Also described are the well-organized force of over 400,000 French Army (only 140,000 of them actually French-speaking) that marches quickly through the Russian countryside in the late summer and reaches the outskirts of the city of Smolensk. Pierre decides to leave Moscow and go to watch the Battle of Borodino from a vantage point next to a Russian artillery crew. After watching for a time, he begins to join in carrying ammunition. In the midst of the turmoil he experiences firsthand the death and destruction of war; Eugène's artillery continues to pound Russian support columns, while Marshals Ney and Davout set up a crossfire with artillery positioned on the Semyonovskaya heights. The battle becomes a hideous slaughter for both armies and ends in a standoff. The Russians, however, have won a moral victory by standing up to Napoleon's reputedly invincible army. For strategic reasons and having suffered grievous losses, the Russian army withdraws the next day, allowing Napoleon to march on to Moscow. Among the casualties are Anatole Kuragin and Prince Andrei. Anatole loses a leg, and Andrei suffers a grenade wound in the abdomen. Both are reported dead, but their families are in such disarray that no one can be notified.
The Rostovs have waited until the last minute to abandon Moscow, even after it is clear that Kutuzov has retreated past Moscow and Muscovites are being given contradictory, often propagandistic, instructions on how to either flee or fight. Count Rostopchin is publishing posters, rousing the citizens to put their faith in religious icons, while at the same time urging them to fight with pitchforks if necessary. Before fleeing himself, he gives orders to burn the city. The Rostovs have a difficult time deciding what to take with them, but in the end, Natasha convinces them to load their carts with the wounded and dying from the Battle of Borodino. Unknown to Natasha, Prince Andrei is amongst the wounded.
When Napoleon's Grand Army finally occupies an abandoned and burning Moscow, Pierre takes off on a quixotic mission to assassinate Napoleon. He becomes an anonymous man in all the chaos, shedding his responsibilities by wearing peasant clothes and shunning his duties and lifestyle. The only people he sees while in this garb are Natasha and some of her family, as they depart Moscow. Natasha recognizes and smiles at him, and he in turn realizes the full scope of his love for her.
Pierre saves the life of a French officer who fought at Borodino, yet is taken prisoner by the retreating French during his attempted assassination of Napoleon, after saving a woman from being raped by soldiers in the French Army.
Pierre becomes friends with a fellow prisoner, Platon Karataev, a peasant with a saintly demeanor, who is incapable of malice. In Karataev, Pierre finally finds what he has been seeking: an honest person of integrity (unlike the aristocrats of Petersburg society) who is utterly without pretense. Pierre discovers meaning in life simply by living and interacting with him. After witnessing French soldiers sacking Moscow and shooting Russian civilians arbitrarily, Pierre is forced to march with the Grand Army during its disastrous retreat from Moscow in the harsh Russian winter. After months of trial and tribulation—during which the fever-plagued Karataev is shot by the French—Pierre is finally freed by a Russian raiding party, after a small skirmish with the French that sees the young Petya Rostov killed in action.
Meanwhile, Andrei, wounded during Napoleon's invasion, has been taken in as a casualty and cared for by the Rostovs, fleeing from Moscow to Yaroslavl. He is reunited with Natasha and his sister Maria before the end of the war. Having lost all will to live, he forgives Natasha in a last act before dying.
As the novel draws to a close, Pierre's wife Hélène dies from an overdose of abortion medication (Tolstoy does not state it explicitly but the euphemism he uses is unambiguous). Pierre is reunited with Natasha, while the victorious Russians rebuild Moscow. Natasha speaks of Prince Andrei's death and Pierre of Karataev's. Both are aware of a growing bond between them in their bereavement. With the help of Princess Maria, Pierre finds love at last and, revealing his love after being released by his former wife's death, marries Natasha.
Epilogue in two parts
The first part of the epilogue begins with the wedding of Pierre and Natasha in 1813. It is the last happy event for the Rostov family, which is undergoing a transition. Count Rostov dies soon after, leaving his eldest son Nikolai to take charge of the debt-ridden estate.
Nikolai finds himself with the task of maintaining the family on the verge of bankruptcy. His abhorrence at the idea of marrying for wealth almost gets in his way, but finally he marries the now-rich Maria Bolkonskaya and in so doing also saves his family from financial ruin.
Nikolai and Maria then move to Bald Hills with his mother and Sonya, whom he supports for the rest of their lives. Buoyed by his wife's fortune, Nikolai pays off all his family's debts. They also raise Prince Andrei's orphaned son, Nikolai Andreyevich (Nikolenka) Bolkonsky.
As in all good marriages, there are misunderstandings, but the couples — Pierre and Natasha, Nikolai and Maria — remain devoted to their spouses. Pierre and Natasha visit Bald Hills in 1820, much to the jubilation of everyone concerned. There is a hint in the closing chapters that the idealistic, boyish Nikolenka and Pierre would both become part of the Decembrist Uprising. The first epilogue concludes with Nikolenka promising he would do something with which even his late father "would be satisfied..." (presumably as a revolutionary in the Decembrist revolt).
The second part of the epilogue contains Tolstoy's critique of all existing forms of mainstream history. The 19th-century Great Man Theory claims that historical events are the result of the actions of "heroes" and other great individuals; Tolstoy argues that this is impossible because of how rarely these actions result in great historical events. Rather, he argues, great historical events are the result of many smaller events driven by the thousands of individuals involved (he compares this to calculus, and the sum of infinitesimals). He then goes on to argue that these smaller events are the result of an inverse relationship between necessity and free-will, necessity being based on reason and therefore explainable by historical analysis, and free-will being based on "consciousness" and therefore inherently unpredictable.