Preludes and Nocturnes opens with a group of dark magicians attempting to summon and imprison Death. Instead, the being who appears is Morpheus, also known as Dream. He is the personification of dreams and lord of the Dreaming, the realm where dreams take form. The magicians keep him prisoner for over 70 years, but eventually he is able to escape.
Although freed, Dream is very weak. His three tools, symbols of his power, were taken from him. He visits the three Fates to learn where to look for each object, and then goes in search of them.
The majority of the book is concerned with his quest for these three tools. He visits various characters familiar in the DC Universe: John Constantine for his pouch of sand; Lucifer and the other demons in Hell for his helm; and the Justice League for his ruby dreamstone.
Dream finds his ruby in the hands of John Dee, or Dr. Destiny, a Justice League villain who is now the only person capable of using the ruby. Dee refuses to give up the stone, and uses it to try to kill Dream. During the fight Dee destroys the ruby, thinking that he will also destroy Dream, but instead all of the power Dream had transferred into the ruby was returned to him and he was made more powerful than ever, easily able to defeat Dr. Destiny.
The final chapter is a conclusion or epilogue to the main story, in which Dream meets with his sister, Death, and finally gets over the experience of having been imprisoned for so long.