One of my favorite novels is William Sleator's "House of Stairs". I've read it like three times over the years. But it never occurred to me to look up any other books by Sleator. Mostly because I thought "Stairs" was a fluke, that is, Sleator rarely wrote science fiction and HoS was the only one he ever worked in that genre. While at a local thrift store, I happened to see a copy of this book, "Marco's Millions" and after reading the blurb on the back of the book, seeing it was yet another sf novel (apparently, Sleator was a science fiction writer. Something I never knew.), I decided to try it out.
I gotta say it's not as good as "House of Stairs". The first half of it, anyway. In the second half, it picks up and improves greatly.
In "Marco's Millions", Marco and his sister, Ruth, discovers a doorway to another world in the basement of their house. Marco travels in it to discover a race of insect-like beings who worship a naked singularity and perform various rituals to appease the singularity, known also as "the Lord" and "the Unknowable". The Unknowable is threatening to erupt and destroys life not only life on the insects' universe, but possibly Marco's as well. They require Marco's psychic sister, Lilly, to act as a medium, or go-between, to set things right. Because she is shy and timid, Lilly is afraid to go to the insect's universe to help. Instead, it is Marco who makes the journey to fulfill the quest.
As I said, the first part of the book drags a bit . It is only when Marco finally goes to the other universe to actively begin the quest, that the novel takes off. The second half of the book more than makes up for the dullness of the first half for me.
"Marco's Millions" does reference "House of Stairs". One of the alternate universes Marco sees when he is near the Unknowable, is a world of nothing but stairs. Also like "Stairs", rituals must be enacted in order to appease an authority figure and the world the teenagers in "Stairs" come from is an impoverished dystopia, while Marco's family is extremely poor.
Incidentally, the concept of a hidden doorway leading to an alternate world reminded me a little of the Harry Potter series (how you get to Hogswart), but mostly it felt like Neil Gaiman's trope. How many of Gaiman's novels are based on the idea of a secret passage to another world? ("Neverwhere", "Coraline".)
But while "Marco's Millions" won't replace "House of Stairs" as a favorite, it does make me curious to read more of William Sleator's novels, particularly "Boxes", the book "Marco's Millions" is the prequel to.