Imaginative novel in which the orator Plato, living in AD 3700, looks back to the past, to a London long since vanished. When he returns with stories of this lost world, however, he is accused of corrupting the young and is put on trial. The chief interest of using tomorrow to comment on today is the flashes of unexpected insight. The author has fun, too, at the expense of our experts' capacity for creating whole cultures from a bit of bone or a few fragmented words: the culture of America deduced from the tales of Edgar Allan Poe is my favourite. That our view of ourselves, our civilization and our world is as partial and flawed as any in the past is a theme of science-fiction writers, and here it is persuasively developed: to give a hefty wrench to present 'received opinion' is an achievement. Is this science fiction? Who cares! - that edifice has by now so many mansions that definition has been outrun by burgeoning creativity, always creating new forms. One never knows where it will break out next. Interesting how many writers are envisaging the end of the age of machines, as if a kind of Walpurgis Night of Luddite fury is brewing in the collective unconscious: while the planners are dreaming up ever more complicated electronic Utopias, the writers seem to be saying that this is all nonsense. The future's definitions of our catchphrases are not the least of the book's pleasures. 'To see red - to see into the fire at the heart of all things.' 'Organ grinder - a kind of butcher.' 'Rock music: the sound of old stones.' 'Dead-end: a place where corpses were taken.' Review by DORIS LESSING Editor's note: Doris Lessing is the author of many novels, including Love, Again and Mara and Dan. (Kirkus UK)