First in a duology by Paul Edwin Zimmer (who apparently was proud of saying "There is no third book!). It chronicles in painstaking detail the political collapse of the human lands bordering a region of demons, goblins, and evil after the young king is kidnapped and replaced by his demon raised twin.
The story is grand, I am not sure I have ever read a better account of sword and siege warfare. Zimmer was a fencer/swordsman so the individual fights are quite detailed. The story-telling itself may suffer some from the militant focus, but it is thoroughly enjoyable.
The tale continues in King Chondos' Ride... | 
