William Tenn 
Of Men and Monsters [EPUB ebook] 

Giant, technologically superior aliens have conquered Earth, but humankind survives — even flourishes in a way. Men and women live, like mice, in burrows in the massive walls of the huge homes of the aliens, and scurry about under their feet, stealing from them. A complex social and religious order has evolved, with women preserving knowledge and working as healers, and men serving as warriors and thieves. For the aliens, men and women are just a nuisance, nothing more than vermin. Which, ironically, may just be humankind’s strength and point the way forward.