Knight of Shadows by Roger Zelazny

Merlin confers with Jasra and Mandor after the assault on the Keep and finds out quite a bit more about what's been going on behind the scenes all these years. A rather fun scene takes place when Mandor is revealed to be a specialist in the sorcery of haute cuisine - he conjures up a wonderful meal on a veranda overlooking one of the realms at the Keep. It turns out that Jasra was responsible for training Merlin's ex, Julia, in the art of sorcery, and that Julia's natural talent caught her by surprise, leaving her as a coat rack.

Julia has allied with Merlin's brother, Jurt, who has had homicidal intentions towards Merlin for a long time, but which have gotten more intense recently as the struggle for succession in the Courts of Chaos has heated up due to the frailty of Sawall, Duke of Chaos. Julia and Jurt have performed a ritual which gives him amazing powers, that Brand (Jasra's husband of sorts) underwent long ago, explaining his near invincibility in the first Amber series at last.

We got set up by Zelazny in the previous book for a shaggy dog type of pun or two here. The chaos demon that serially possesses people near Merlin, the ty'iga, turns out to be named for a specific purpose - so that Merlin can shout, "Hold that ty'iga" at one point and then shortly later, to have to choose between the lady or ty'iga. Groan.

So, as we learned in the previous book that the Pattern is actually sentient, we might surmise that the Logrus (Chaos' version of the Pattern) is also sentient. It appears that they have been in a large scale conflict for ages, and they force Merlin to participate in one of their battles for dominance. He is spirited away to a place or state of being where none of his magic works, the Trumps are dead, and he can't manipulate shadows. There he faces a number of challenges and opponents. Some of these creatures are Pattern-ghosts or Logrus-ghosts.

Whenever a person walks the Pattern (or Logrus) they are "recorded", and can later be reproduced by the Pattern or Logrus, in the same state they were the day they finished walking. So, Merlin is visited by Deirdre, slain by Brand in The Courts of Chaos, Oberon, dead in the same book, an earlier copy of his brother Jurt, his father Corwin (who may not actually be a ghost), Dworkin (thought to be dead) and several others on his quest. Merlin refuses steadfastly to take sides in the conflict, but is tricked into mostly championing the cause of the Pattern.

This one gets pretty surreal for a while before dropping back into a more "normal" narrative. Eventually we get back to the main story, find out what Luke and Dalt have been up to, and solve a few more mysteries.