By Nadine Gordimer

Farrar Straus and Giroux. 277 pp. $19.95

"IT'S NOT so long since you learnt to change the idea you had of yourself as powerless against whites," Hannah Plowman, a white woman and a monitor of human rights abuses in South Africa, reminds Sonny, her mixed-race lover. "The old Left did it, by god . . . Now new realities {have} to be accepted . . . It means the loss of absolutes."

The discomfiting dissipation of absolutes is at the heart of My Son's Story, Nadine Gordimer's 10th novel and 18th work of fiction. The new and changed realities corrode family traditions and personal morals. They force decent citizens into deceitful lives of self-indulgence and betrayal. Police surveillance, pre-dawn raids, detention and harassment of civil rights activists: These are givens, of course. But the shameful injustices and the brutal apparatus of apartheid are, this time, merely the context for Gordimer's relentless scrutiny of our capacity for self-deception. The pre- and post-detention domestic life of a freedom-fighter is the narrative's focus.

The emotions detailed -- filial competitiveness, sibling rivalry, adulterous passion -- are intended to be familiar, if not banal. The tragedy (and this is a profoundly tragic novel) is that, in Sonny's and Hannah's South Africa, ordinariness is a luxury that the revolution denies to men it has groomed to be its icons.

Gordimer fuses Aristotelian and Shakespearean tragic visions into one that is contemporary and credible. Well-intentioned men and women are impelled into disaster because they obey "the . . . law of life: moving on." To impede change is to go against nature, to challenge destiny. Catastrophe comes more swiftly, and more harshly, to those who are burdened with character flaws, such as an excess of innocence or ambition or oedipal envy.

Gordimer provides Sonny, a school teacher-turned-activist, with an embittering rather than cathartic insight at the end of the novel: "In a school teacher's safe small life, aphorisms summed up so pleasingly dangers that were never going to have to be lived. There is no elegance in the actuality -- the distress of calumny and self-betrayal, difficult to disentangle."

Free will, the exercise of options -- these are illusions. Will, the teenage son of the title, understands this better than his parents: "I'm going to be the one to record . . . what it really was like to live a life determined by the struggle to be free . . ."

Will is named after William Shakespeare by Sonny, his autodidact father. The family includes Aila, Will's homemaker mother, and Baby, his headstrong sister. One afternoon Will catches Sonny coming out of a movie-theater with Hannah, the white activist, and decides that Sonny's affections for Hannah are adulterous. This traumatic encounter becomes the starting point of his career as a writer. In the age of "new realities," the angry and biased teenager, not Shakespeare, is the fit chronicler of disintegrating morals.

Will insists on remembering his childhood -- in a settlement reserved by the government for those it classifies as "colored" -- as an idyllic one. Sonny was once a happy family man who took his wife and children picknicking in green spaces speckled with mine-dumps. Will's misguided point is that if his father had not been cursed with a social conscience and a demagogue's charisma, he would not have moved out of the ghetto, would not have become a political prisoner and Hannah's lover.

Hannah Plowman, pink, overweight, flabby as a milk-pudding, Will mis-presents as a primordial villain. In his account, Hannah invades the family disguised as a do-gooder, seduces and then dumps Sonny, and finally moves on to a more glamorous job with the United Nations. The fallout of her seduction is dire: Baby attempts suicide; Aila becomes a terrorist leader's courier; Sonny loses the respect of revolutionary leaders.

Gordimer's narrative strategy is complex, and purposely misleading. She sets up two distinctive "voices" -- one omniscient, the other subjective and unreliable -- then fuses them in the final section. Will-the-writer forgives Sonny's weakness and betrayal, Will-the-son doesn't. Will-the-son explains Sonny's shuffling between Aila and Hannah as a crude conflict between duty and desire. But Will-the-writer invests Sonny's need for Hannah Plowman with resonance.

"Needing Hannah. His {Sonny's} attraction to Hannah belonged to the distorted place and time in which they -- all of them -- he, Aila, Hannah, lived. With Hannah there was the sexuality of commitment; for commitment implies danger, and the blind primal instinct is to ensure the species survives in circumstances of danger, even when the individual animal dies or the plant has had its season."

The final view of revolutionaries is startlingly unsentimental. At 52, Sonny is a sad, silent, powerless ex-schoolteacher and ex-militant, with enlarged prostate and decayed gums. The political leaders who endure are the ones who are willing to throw away their guerrilla fatigues and compromise with Pretoria, to wheel and deal over expense-account lunches.

In My Son's Story, Nadine Gordimer has given us a work of bleak beauty and enormous force.

Bharati Mukherjee teaches English at the University of California, Berkeley. Her most recent work of fiction is "Jasmine," a novel.