This synopsis will contain spoilers!
Sanshirō is a young man from rural Japan heading to the university in Tokyo where he will continue his studies in literature. While on the way he meets an older gentleman who discusses the approaching downfall of Japan. He also meets a woman who makes a sexual advance towards him, but when he doesn't reciprocate, she laughs and call him a coward.
At the university he makes a few friends, and discovers that the old man (Hirota) is a professor at the school. He slowly falls in love with a young woman named Mineko, but never makes a formal profession of his interest. At times she seems to feel the same, but at others she is aloof to him.
One of Sanshirō's closest friends lives with Hirota, and begins a campaign to make Hirota the first Japanese professor of English in the university. The campaign backfires, however, and Sanshirō is accused of writing a piece of propaganda in favor of Hirota's advancement. Hirota doesn't seem particularly interested in the effort on his behalf, nor upset about it when it fails.
One night during a walk Sanshirō tells Mineko he wanted to see her, specifically, but the moment is soon lost. Soon after Sanshirō hears that Mineko is now engaged to be married. His best friend Yojiro tells him there are plenty of other women, and he shouldn't worry about it. He was too young for a girl like Mineko, who needs a husband who is already accomplished and established. The book ends with Sanshirō seeing the painting that was made of Minkeo. When asked what he thinks, he replies with a reference to one of their early moments together.
Natsume Soseki the First Line of Sanshirō
Natsume Soseki the Last Line of in Sanshirō