Ah, how the memories come flooding back! The Doll's House was definitely my starting point with The Sandman. I read the issues that comprise the Preludes & Nocturnes tpb as back issues after working my way through The Doll's House.
After repeating "The Sound of Her Wings," which closed out the last collection, we get "Tales in the Sand," which adds a crucial bit of ancient backstory to Dream's saga. Told as an African folktale passed down through the oral tradition as part of a coming of age ritual, the story of Morpheus's forbidden love for the human queen Nada will come to have larger consequences in the overarching narrative--but we'll get to that in later issues as it comes up.
"Tales in the Sand" also has a more immediate effect because it potentially changes how we view Dream as a character. When Morpheus condemns Nada to torture in Hell for what he perceives as her rejection of him, it both adds to what we know about his character and diminishes him in our view. While the Dream of past issues seemed aloof, angsty, and somewhat unknowable, it was still easy to forge a line of sympathy between him and the reader. "Tales in the Sand" changes that; here we see Dream acting petulant, demanding, and cruel. We see that he is more than just the brooding hero of the series. He is flawed, deeply so. Our sympathy for him has to alter because it is touched by now knowing that his passions can run self-centered and imperious.
Is Dream a full-fledged Byronic hero? It's a possibility well worth keeping in mind as the series progresses.
After the prologue of "Tales in the Sand," The Doll's House sets upon two intertwined plots: Morpheus tracking down four errant dreams who escaped his realm while he was imprisoned by the Burgess family and Rose, who is a a "dream vortex," tracking down Jed, her missing brother. These two plot lines are intertwined because Rose is the granddaughter of Unity Kincaid, a woman who succumbed to the "sleepy sickness" when Morpheus was trapped in the Burgess's house; both the escaped dreams and Rose's status as a vortex are tied to Dream's captivity.
The narrative strands converge at a "cereal convention," which is really a clever, dark ruse for what is, in fact, a convention of serial murderers. (The latest season of American Horror Story, Hotel, "borrowed" the serial killer party idea something fierce.) I love the cheeky send-up Gaiman gives to serial killer fanboys; the real serial killers catch a wanna-be 'zinester (who I am pretty sure is a pointed mockery of Peter Sotos; the fictional counterpart writes a 'zine called Chaste, while Sotos wrote an infamous serial killer 'zine called Pure) in their midst and show him what cold-bloodedness is really all about.
Since Rose is the dream vortex--a force that threatens to undo the chaotic order of the dreamworld--it is Morpheus's duty to kill her to keep his realm from collapsing and taking humanity along with it. Until, of course, Unity Kincaid steps in and assumes her rightful place as the vortex in an act of self-sacrifice that preserves Rose's life. As it turns out, Rose being positioned as the sacrificial vortex was a stratagem on the part of Dream's sister-brother Desire, another of the Endless.
After the fact, Morpheus learns a horrible truth: Desire had fathered Rose's mother on the sleeping Unity, and if Dream had killed Rose he would have been guilty of killing one of his own blood. Why that crime is so portentous isn't clear at this point in the series, but there are two items of Sandman lore worth keeping in view after the events of The Doll's House: taking the life of one of Endless blood is an unpardonable crime and the three witch horror-hosts of The Witching Hour have appeared in this section of the story to hint at another function they serve--that of avenging furies, the Kindly Ones.