Napoleon invades Russia and preparations begin for another great battle against him.

As the French army marches east, Marya is terrified to discover that her family is in danger and her father is refusing to listen.

Natasha falls ill and Pierre helps care for her before making a decision that opens his eyes to the horrors of war. Andrei finds he cannot forgive Natasha, and vows to take revenge on his rival. Meanwhile, Helene struggles to manage a compromising situation.