What is the author's tone in The Martyr by Ngugi wa Thiong'o?

This particular narrator adopts a tone of almost exaggerated sarcasm in conveying the racist attitudes of the white European settlers. For instance, in describing Mrs. Hill's sense of herself as generous and kind toward the Africans who work for her, the narrator uses sarcasm to emphasize the self-congratulatory attitude of the "liberal" settlers, who felt themselves to be doing a favor for the Africans.