Need help to Find Fantasy/Scifi book and author


Hi there, just joined because its been bugging me for years that I can't find this great book I read back in the late 80s/ early 90s.

The book is a fantasy/ sci fi with good vs bad, demons, vampires, devils and so on.

It starts out that there is a person/thing who can see the true nature of everyone and he figures out that a messinger is lying and telling the king something not true that will mess up the good side. It goes on and there is standard stuff about evil gaining gound and being sneaky.

Then there are big battles and the evil (devil?) is breaking out of his shackles.

The thing that was neat was that in this major battle between the armies of good/bad, even Death took sides, he was on the side of good and would kill off the bad guys slightly sooner than the good guys so as not to be too noticible to everyone else. This made a vampire mad when he was about to enslave some guy and the guy bit down on some poison, killing himself (with the aid of Death) before he could be bitten. So its not really about vampires but there are vampires in there fighting for the bad side.

any ideas?