A solid journalistic re-creation--no startling new information, no particular point--of the worst single day for London in World War II. Four days after Christmas 1940 the German bomber command set London ablaze in the greatest fire since 1666: Hitler, incensed by the RAF's reprisal raids on Berlin, chose as his vengeance target the tightly crammed, combustible City of London district at the heart of the metropolis. Guided by their new X-beams, the Luftwaffe's lead group--with incendiaries to create a bull's-eye blaze and make way for a second wave of high-explosive-carrying bombers--set off, aiming for St. Paul's Cathedral. And the City business district, near-deserted on a Sunday evening, was near-helpless when dry old buildings went aflame--especially since the tide in the Thames was out, fatally lowering the water pressure. London's early fire fighters found themselves in chaos; broadcaster Edward R. Murrow said, in his voice-of-doom Sunday-night report to the US: ""Tonight, the bomber planes of the German Third Reich hit London where it hurt most--in the heart."" Anti-aircraft guns were a total failure (though a fine morale builder), flak never hitting the bombers, dropping steel pieces an utter menace; guns had to be called off when RAF fighters went aloft. One could read a paper by the crimson glow of the fire; in one church John Milton's bones baked to dust. Johnson has no central focus here, turning his attention from the German decision-makers to people-in-the-street to pilots and firemen and politicians. But, with dozens of witnesses contributing brief reminiscences, it's a vivid evocation in the sturdy you-are-there manner.