Imagine an enormous Universe, millennia from now. Within the Universe, there are many worlds, The Middle Worlds. Most of these worlds are inhabited by more or less intelligent creatures, not all of them human, though. At the beginning of the book, the Universe is ruled by two 'Houses' of Power, The House of the Dead and The House of Life. Osiris, Master of the House of Life, supports life whenever he can, while Anubis, Master of the House of the Dead, strives to destroy it. The Middle Worlds are constantly torn between the two Houses: plenty, proliferation and overpopulation on the one hand, famine, plague and annihilation on the other, mainly resulting in a dubious sort of equilibrium.
After having been a faithful servant in the House of the Dead for one thousand years a man, whose name was taken from him long ago, is summoned by Anubis. He is given a new name, Wakim, and is then sent to the Middle Worlds as Anubis' emissary, to seek and destroy an immortal, presently known as 'The Prince Who was a Thousand'. Meanwhile, in the House of Life, Osiris orders his son, Horus the Avenger, to descend to the Middle Worlds, and kill 'The Prince Who Was a Thousand' in his name.
This is how the story begins. A truly fascinating one, about Egyptian gods, witches, immortals, supernatural beings, magicians, machinery, computers, and betrayal. Quite a complicated story, too, mainly because the reader is, for quite some time, kept in the dark about the true identities of some of the protagonists. Some of the gods possess various identities and others are -due to an anomaly in Time- each other's father and son at the same time, which is quite confusing.
Taking into account that the book was written in 1969, the concepts of 'temporal fugue', a martial art using the fabric of Time and 'Skagganauk Abyss', a phenomenon which is now widely known as 'a black hole', show that Zelazny was definitely ahead of his time.
Roger Zelazny, he died in 1995, was one of the greatest and most inventive SF/fantasy writers of the 20th century. In 'Creatures of Light and Darkness' he has managed to combine various elements of science, fantasy, mythology, ideology and SF in one story, without violating its credibility in any way. Just before he wrote 'Creatures..." Zelazny had won the Hugo Award for his masterpiece 'Lord of Light', which still is one of the best SF books ever.