The narrative frame of the entire story is the unnamed narrator writing about his experiences with Sensei an unknown length of time after Sensei's suicide. However, out of modesty, she refuses to elaborate, and the two leave the matter when Sensei returns. Then Sensei's wife, with tears in her eyes, asks the narrator whether he thinks she is to blame for Sensei's unhappiness the narrator disagrees to this too, which prompts Sensei's wife to recall the incident in Sensei's past after which he changed from an energetic young man to a melancholic: a student friend of his died, and not by natural cause. Sensei's wife says she believes Sensei must dislike her too, because she is part of the world he dislikes, but the narrator disagrees and senses that even she does not believe this. The two begin to talk about Sensei, and the student wonders about the relationship between Sensei's general weariness for the world and his love for his wife. Over time, the narrator becomes the most regular guest at Sensei's quiet household, and one evening he stays there alone with Sensei's wife in order to protect her in Sensei's absence. One day while walking in a park, Sensei tells the student enigmatically about guilt in love, but refuses to explain further. Moreover, despite the strong love that exists between Sensei and his wife, the narrator learns from one occasion when he hears Sensei having an argument with her that Sensei feels she will never completely understand him. Though Sensei lives comfortably with a beautiful wife, Shizu, who is the like the ideal of a kind and obedient spouse, he is intensely melancholic and reclusive, and often speaks critically of himself, alluding to what the narrator discerns is a past tragedy while concealing most details. The narrator begins to visit Sensei more often and, his respect and interest in the man growing with each of their conversations, he tries to come to an understanding of him. Sensei is uncomfortably surprised to see the narrator, and, refusing to reveal the full significance of the graveyard he visits monthly, only tells him that a friend of his is buried there. Back in Tokyo, he calls on Sensei, but finds that the man has gone to a nearby cemetery at Zoshigaya and so he follows him. While aimlessly frequenting the beach alone, he notices and then befriends an enigmatic older man, whom he impulsively calls Sensei.

During a summer holiday at the beaches of Kamakura, a city near Tokyo, the narrator, then a university student, is left alone when his friend is forced to return home. The novel begins with the unnamed protagonist writing about his past experiences with a man whom he called ' Sensei' ('teacher' in Japanese).

Kokoro soseki