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 proposes marriage with Prince Kuragin's beautiful and immoral daughter Hélène (Elena Vasilyevna Kuragina), to whom he is sexually 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 has an affair with Dolokhov, who mocks Pierre in public. Pierre loses his temper and challenges Dolokhov, a seasoned dueller and a 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 and confuses 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. At the Battle of Austerlitz, Andrei is inspired by a vision of glory to lead a charge of a straggling army. He suffers a near fatal artillery wound. In the face of death, Andrei realizes all his former ambitions are pointless and his former hero Napoleon (who rescues him in a horseback excursion to the battlefield) is apparently as vain as himself.
Prince Andrei recovers from his injuries 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 and help solve some of the problems of Russian disorganization that he believes were responsible for the loss of life in battle on the Russian side. Pierre comes to visit 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 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 Anatol. 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 Anatol conspire together to accomplish this plan. Anatol kisses Natasha and writes her passionate letters, eventually establishing plans to elope. Natasha is convinced that she loves Anatol 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 shocked and horrified at Natasha's behavior, but comes to realize he has fallen in love with her himself. During the time when the Great Comet of 1811–2 streaks the sky, life appears to begin anew for Pierre.
Prince Andrei accepts coldly Natasha's breaking of the engagement. He tells Pierre that his pride will not allow him to renew his proposal of marriage. Shamed by her near-seduction and at the realisation that Andrei will not forgive her, Natasha makes a suicide attempt and is left seriously ill.
