The main narrator of My Son's Storyis Will, who finds out that his father is keeping a white woman as a mistress. Due to the social and racial stigmas of 1990s South Africa, this is a very big deal, and it changes Will's perceptions of his family life and his view of the world at large.
There was my father; the moment we saw one another it was I who had discovered him, not he me. We stood there while other people crossed out line of vision. Then he came towards me with her in the dazed way people emerge from the dark of a cinema to daylight.
(Gordimer, My Son's Story, Google Books)
In that scene, both Will and his father realize they they are each deceiving each other; Will is skipping study time to watch a movie, and his father is having an affair. Through this initial discovery, Will loses his childhood innocence and his respect for his father's ideals. Portions of the story are also narrated by Will's father, and by Hannah, the white mistress; this allows the story more justification than Will's single, very personal viewpoint.