The City of Lankhmar, in the world of Nehwon, is threatened from within by a force so cunning, so smart, and so massive that it is amazing how invisible it is to all who live in the city. Yet nobody will realize just how much danger they are in till Fafhrd and the Gray Mouser stick their noses into the plot - and make it even a bigger mess.
As many reviewers have pointed out, it is kind of hard to cheer for either side. The invaders, in some ways, seem smarter and more loyal to their cause then the city's own Royal Family and nobles are. In fact King Glipkerio is unbalanced, sick in mind, and not very interesting to look at either. The people he surrounded himself with just enable his twisted delights with their own actions. I am surprised nobody had assassinated him before these.
We also get to meet the Gods OF Lankhmar, who frankly, don't put up as much of a show as one would have wished.
Ghouls, a two-headed dragon, a man from another words, we get a lot of action, adventure, humor, and thrills, for our buck. I think most of that has to do with it being a full length novel and not just a short story.
If you enjoyed this book, or the Swords series as a whole, may I also suggest a few other books. First off, there is the character of Conan whose adventures are collected in three books ; The Coming of Conan the Cimmerian: The Original Adventures of the Greatest Sword and Sorcery Hero of All Time!, The Bloody Crown of Conan (Conan of Cimmeria, Book 2) and The Conquering Sword of Conan (Conan of Cimmeria, Book 3). Then, if you prefer a longer, more modern series, in the form of short stories, may I suggest at least getting the first of the hardcover Thieves' World books - Sanctuary: Thieves' World; Tales from the Vulgar Unicorn; Shadows of Sanctuary which holds the first three paperback books in one edition. In fact, there are hundreds of titles, and I can't list them all. Enjoy!