I looked at the copyright page and found that it was first published in 1968, but it has the flavor of earlier science fiction. In fact, it reminded me of a story I read in an anthology edited by Isaac Asimov called Before the Golden Age which included Science fiction stories published in the 1930s. The story was Tumathak of the Coridors and I would not be surprised if Of Men and Monsters was based on it. In both stories humanity has been defeated by invading aliens and reduced to living in dark recesses. In the earlier story it was in coridors that were apparently underground. In Of Men and Monsters it is in burrows the location of which comes as a surprise so I won't give it away here. Humans have taken on a symbiotic relationship with the aliens. They raid the alien larders for food and they live in close proximity with the aliens even though if the aliens had their way they would destroy the humans. In other words, humans have become the aliens' mice. Most humans long for the overthrow of the aliens and a return to their dominence over the Earth, but it is gradually realised that they are actually thriving under alien domination. That leads, in the end, to another solution. It is a solution that does not overthrow the aliens,but for those of you who root for the humans, don't worry. It is a solution that the aliens will not like in the least.