Sign of the Unicorn — Roger Zelazny

Amber, the one real world, of which all others--including our Earth--are but Shadows...

A traitor has revealed the royal family's greatest secret--the ability to manipulate Shadow and travel among all possible worlds--to forces that plot Amber's destruction. And Corwin, prince of the blood, must risk all in a deadly assault on evil's stronghold.

Now, beset by demonic powers beyond imagination, betrayed by a bizarre conspiracy among his own kin, Corwin walks a perilous path toward ultimate knowledge and terrifying discovery.