El Salvador, 1982, is at the height of a ghastly civil war. Joan Didion travels from battlefields to body dumps, interviews a puppet president, considers the distinctly Salvadorean meaning of the verb ''to disappear'' and trains a merciless eye not only on the terror there but also on the depredations and evasions of US foreign policy. Salvador is a restless and unflinching masterclass in the art of reportage by one of the great literary stylists of the twentieth century.