Lessing’s 22nd novel, a dystopian allegory set in “Ifrik” (formerly Africa) thousands of years hence, is a ponderous, hectoring, fascinating second cousin to her Memoirs of a Survivor (1975) and The Four-Gated City (1969) (and quite reminiscent, incidentally, of Norman Mailer’s similarly forbidding Ancient Evenings). After a global war and second Ice Age have decimated the continent and a more recent drought has made “civilization” only a distant memory, two children, seven-year-old Mara and her younger brother Dann, are abducted and forced to join a slow northward migration, toward water and the remnants of destroyed cities. As they grow to adulthood, together and apart, both are subjected to numbingly repetitive ordeals: capture by conflicting “armies”; enslavement for various purposes (Dann suffers both drug addiction and homosexual rape, while Mara is exploited as a spy and as a “breeder”); and hairbreadth escapes (rather too many) from their several oppressors. Eventually reaching a northern territory where specific knowledge of their culture’s past is available, Mara and Dann learn the secret of their own origin—and the duty they were born for but now reject. Neither plot nor characterization is Lessing’s strongest suit, and the story’s climactic developments may strike some readers as willful overkill, but this often frustratingly turgid tale generates considerable power nevertheless. The world Lessing’s opaque protagonists inhabit has been imagined in weirdly convincing detail: cities (“as temporary as dreams”) lie drowned beneath scarce remaining rivers, which run shallow and are infested with “water dragons” (crocodiles) and other exotic predators; men struggle for dominion over exhausted land; and women scheme to outwit male “rulers.” The powerful, almost erotic attraction between brother and sister is virtually palpable—as are Mara’s fierce hungers: to give birth, be loved, and learn the history of the world crumbling around her. As demanding and intermittently infuriating as anything Lessing has ever written—and as necessary. She isn’t a stylist, and she takes no prisoners, but this writer remains one of contemporary fiction’s genuine thinkers and visionaries, and it would be folly to ignore her.