Del Rey, Lester
DAY OF THE GIANTS
Day of the Giants, by Lester del Rey. Magazine version was titled "When the World Tottered" in Fantastic Adventures December 1950. The first book appearance was an Avalon hardcover in 1959.
Leif Svensen's neighbor, come to warn him that the farmers were going to take violent action against his dog for killing their livestock, mentioned that he'd seen an angel the night before. "Big blonde woman on a white horse, singing loud enough to wake the dead, about a hundred feet up in the air." Then, on his way to find his madcap twin, Leif met the stranger who knew his name who spoke of the "the Fimbulwinter already upon us." Fimbulwinter was the dreadful winter that in Norse mythology preceded Ragnarok - the final war between the gods and the giants! Leif Svensen and his brother were caught up in the destinies of a real but alien world. For if the giants triumphed, they would overrun Earth; and if the Aesir - the gods - won, Earth would be their footstool.