Tuck Underbank is a Warrow -- think a hobbit with shoes and "large jewel-like eyes" -- living in the peaceful Boskydells. When an unnaturally cold winter strikes and the evil Modru threatens the world, he and a number of his fellow Thornwalkers go to the High King's aid. But a vast expanse of lightless blizzard called the Dimmendark (sounds bad, doesn't it?) is spreading over the land, and Tuck soon finds that the "dark tide" is going to swamp them all.
Despite the fact that they're tiny and temperamental, the Warrows get included in the military forces. But the High King doesn't have enough warriors to hold off the horde of slobbering monsters who are coming to attack. And the battle goes horribly wrong, separating the friends from one another and possibly dooming them all.