The novel centers around Augustin Meaulnes, a new student to the school in the little village that Francois lives in in the Sologne region of France. Augustin is 17 years old and is intelligent and comes from a modest upbringing; he is very tall so gains the nickname of 'grand'. However, one evening he runs away despite being the class hero and favorite, and he ends up getting lost.
He manages to stumble across a strange costume party that is being held to celebrate Frantz and Valentine, who are about to get married together. While at the party, Augustin meets Yvonne de Galais, who he instantly falls in love with as she is the girl of his dreams. Unfortunately, Valentine does not show up to the party, and as a result, Frantz tries to kill himself, but he fails.
When Augustin returns from the party he longs to find Yvonne again, however his search for her fails. One day, another new student appears at his school. The student is Frantz, although he is using a different name, and he becomes friends with Francois and Augustin. Frantz gives Augustin Yvonne's address, in Paris, so that he can find her. However, it turns out years later than Yvonne never moved to Paris as instead, she cared for her dying father.
Augustin finally meets Yvonne again and they agree to marry each other, yet days later Augustin leaves her to find Frantz and reunite him with Valentine. While this is happening, Yvonne gives birth to a baby girl, only to die a couple of days later. The young girl is raised by Francois until Augustin returns and finds out that Yvonne is dead, so he looks after their daughter.
