Sign of Chaos is the eighth book in the Amber saga by Roger Zelazny.

This book continues the narrative of Merlin, son of Corwin.

Wikipedia contains spoilers

Merl sets out to aid his friend Luke and gets tied up in a psychedelic experience which involves characters from Alice in Wonderland. Afterwards he embarks upon an attack of the Fortress of the Four Worlds, where he discovers the identity of his enemy.