In the Sign of Chaos, Zelazny turns the magic of his sorcerous Logrus initiates loose in a big way, including a very entertaining sequence where Merlin, his very interesting half brother Mandor, and a surprising third ally make an assault on the Keep of the Four Winds. Spells and fur fly, and in the end Merlin finally gets a handle on who all the players may be in his troubles through these books, if possibly not a clear picture of all their motivations. We also see more interaction with the Ghostwheel.
As with both five book Amber series, Sign of Chaos does not stand on its own. It is, fittingly, just the middle of this very intricate series of mysteries and adventures.
Zelazny's writing continued to entertain in a way separate from the plot itself. For example, he gives Merlin very clever and amusing names for his spells. Merlin continues to be a fascinating combination of spunky and naive, taking great pains to follow his own agenda despite what those around him might prefer. Many of Zelazny's characters from the first Amber series play interesting roles, along with new, vibrant characters introduced here with Merlin's story.
I'm having a terrific time reading these books again. As I write this review I'm halfway done with the final book, and I'll be a bit sad to be done with them.