Fantasy book featuring shifting doppelgangers as spies and assassins

Question

I'm trying to find a book that I read in (probably) the late 90s where the enemy would employ doppelgangers as one of their ultimate weapons to infiltrate, spy, and assassinate. I think that the doppelgangers had to kill their target in order to take on their shape/face.

The doppelgangers were not the main focus of the story. The enemy employed others as well... I vaguely recall a fireball and a doorway.

I think the main character stayed fairly central to one location (a castle) and that it wasn't a book with many, if any, journeys.

Unfortunately, I really don't remember a whole lot, and even the above was stretching.

Answer 1

This sounds like a series of books by Kristine Kathryn Rusch called The Fey. It is a series of five novels, which were written in 1995-1998. In the series, the Fey are an invading force which have concurred three continents and now try to take the Blue Isle. The Blue Isle, however, has formidable barrier mountains which ring the exterior of the isle, thus keeping the inhabitants safe ... until the Fey invade. The Islanders discover they have a weapon of holy water which, when it touches a Fey, kills them by dissolving them. In the first book, this defeats the invading force of the Fey, but doesn't kill the Black King's obsession to concur the Isle.

The doppelgangers, as you describe, are quintessential to the story, yet are not the focus. The only way you can tell if a person has been taken over by the doppelganger is their eyes will have golden flecks. When a doppelganger takes over the body and identity, they gain all of the knowledge of the individual in the process. Their magic is considered to be amongst the most powerful of the Fey.