Spoiler alert: This post is part of an in-depth discussion of The Hand of Oberon by Roger Zelazny, which will inevitably reveal key plot points. I recommend you support your local bookseller or public library, and read the book first.
After a trip to the ghostly, floating city of Tir-na Nog'th, Corwin, with his brother Random and general Ganelon, were led by a unicorn to a place that appeared to be Mt. Kolvir, but with the top of the mountain and the palace missing, and only the Pattern remaining. They realized they were looking at the primal Amber and Pattern.
The Pattern was marred with black splotches, and at the center they found a dagger impaling a Trump of an unknown person. They figured out that the damage to the Pattern was caused by spilling blood of Amber. Random realized that the figure on the Trump was his missing son, Martin.