The Dark is Rising by Susan Cooper
"It's a horrible day," said Will Stanton. "It's creepy somehow."
On the day before his eleventh birthday, Will and his brother escaped from their noisy, happy house into the quiet English countryside. A black wind was blowing just a bit of snow, but there was more to come, snow and blackness both, for the Dark was rising across the land.
They stopped to get some hay at Dawson's Farm. The farmer took Will aside.
"The Walker is abroad... and this night will be bad, and tomorrow will be beyond imagining."
In the summer of 1942, the Japanese were winning their war with the United States. They had sunk or crippled America's battleship fleet at Pearl Harbor, and snapped up a chain of islands across the Pacific which could, if fortified, form an impenetrable barrier to the U.S. Navy. Now the Imperial Japanese Navy was looking for a knockout blow, to destroy the American aircraft carriers before American industry replaced its losses.