Book four of The Chronicles of Amber features Corwin on a trip to the true Amber. He discovers the source of the Black Road and finds out what it will take to repair it. He also determines that his father (Oberon) is still a master strategist. His hand is guiding the pieces into place for the final battle. The final page had a big revelation that had me anxious to read the next book when I first read it.
Rick Sternbach supplied the cover to the May 1976 of Galaxy Science Fiction that featured part 1 (of 3) of the serial. One of the many reasons I loved Jim Baen's time as editor of Galaxy was because he published "Sign of the Unicorn", "The Hand of Oberon", and "The Courts of Chaos". This is not the kind of story you would expect Sternbach to draw the cover for but it is a fascinating different type of cover for him.
The first five books of the original Amber series remains one of my favorite series. It is hard to discuss events from this book without revealing too much.
The author appears as "Roger" a pipe smoking guard in the dungeons of Amber. The guard is writing "philosophical romance shot through with elements of horror and morbidity." This is fitting since one of the main themes is the true nature of reality.
All I will say is that Zelazny plays fair with the big final revelation. When re-reading the series you can see where he planted the clues to this one. Like all good mystery writers, he gave the reader a chance to solve the puzzle.
Anyone who likes fantasy epics, parallel worlds, hard boiled main characters, and great mysteries will love this series. I can not recommend the first five books too highly. The second five are still good but are a step down from the original five.