A novella written by John Steinbeck at the beginning of World War II. Essentially, the story is a literary prototype of Red Dawn; only in this case, the untitled land is being taken over by what are ostensibly Nazis.
One Sunday morning, said village is invaded while all twelve of its troops are on a fishing trip sponsored by the local merchant, Mr. Corell. It turns out that Mr. Corell is a collaborator with the invaders, who are led by a Colonel Lanser. The town's leader, Mayor Orden, has no official recourse, but is vehemently opposed to the conquerers.
Over time, the townspeople, including two former troops who escaped during the village's capture, plot to take back their town. Moreover, the conquerers seem to have won the battle but lost the war of ideas, not to mention morale.
The Moon Is Down is a good read, not to mention extremely short. Such issues as aiding the enemy and individuality are issued in a literary light. If you have an hour or two to kill, and you want to kill some Nazis at the same time, this novella is a good way to do both.
ISBN 0140187464, Penguin, Nov. 1995. Thanks to smokngOat for the info. I used a Viking anthology of Steinbeck's short novels from the fifties.