What is the main conflict in The Martyr by Ngugi wa Thiong'o?

While Mrs. Hill prides herself on her generosity to the Africans who work for her and the loyalty of her "houseboy," Njoroge in fact deeply resents her for her "smug liberalism" and her "paternalism" in these matters. In his small hut that night, Njoroge thinks of his own wives and children, and then of Mrs. Hill's children, who are away at school. Seeing her "humanized" in this light, he is unable to conceive of killing her. He runs to her house to warn her before the Freedom Boys arrive to murder her. Alarmed and suspicious, Mrs. Hill incorrectly believes he is knocking at her door to kill her—and she shoots him in what she believes is self-defense. Thus, "she had in fact killed her savior."