Don DeLillo's compendious new novel begins on the portentous day of Oct. 3, 1951, when two shots heard 'round the world defined and determined the history of America for the second half of the 20th century: Bobby Thomson homers in the bottom of the ninth to beat the Dodgers and win the pennant for the Giants, while half a world away, Russia announces the detonation of its first hydrogen bomb. Nick Shay, a young Dodgers fan from the Bronx, realizes that he must own the baseball. For Shay, Thomson's triumph has paradoxically come to symbolize failure, defeat and entropy itself, and in a world already beginning to metamorphose under the threat of instant annihilation, that baseball is the only thing in the world that he absolutely must own. DeLillo takes us, in a beautifully convoluted way, through the entire second half of this century, trying desperately to hit on every significant detail as his characters struggle to comprehend a changing America. Not everything that changes is visible or immediate, and baseball, the bomb, Frank Sinatra, Vietnam, the interstates, condoms, computers, and dozens of other people and events set resonances which travel through time and space, creating a formless but intimately human picture of our recent past. This is historyanecdotal, not quite nostalgic, and contained in dialogue and private thoughts, the reminiscence of old lovers, and the study of old photographs. For Underworld's inhabitants, the past was not the future they had hoped for, and Shay's search for the baseball becomes a small part of the constant search for meaning in a time which seems to have outgrown every meaning they know. Underworld is a big cluttered basement of a book, a great trash-or-treasure heap of memories and stray feelings in which every scrap means something, or has value, to someoneand in which the oddest scrap of thought can be profound, universal, moving, and magnificently human. Don DeLillo, at the height of his powers as an author, has written an exquisitely beautiful and utterly humbling novel.