Margaret Sinclair turned to writing books in the 1960's. I don't know why her short story output declines after 1960, but I think it may have had to do with monetary reasons. Science Fiction and Fantasy became big sellers in the Age of Aquarius. Authors are often forced to write to pay the bills. Although the genesis of this novel may have been in the back of her mind for years, the second part seems to have been created for the specific era it was written.
The Shadow People is very much a product of it's time (1969), but it has influences which go back to the early part of the last century and beyond. As if Arthur Machen had wandered into the Fillmore Ballroom. Gary Gygax, one of the creators of the Dungeons and Dragons game, lists it as an influence. St. Clair quotes selectively from Robert Kirk's 17th century tract on faeries, The Secret Commonwealth. I suspect she used Commonwealth as a guide while writing this novel.
But enough with my speculations. Dame St. Clair is no longer with us, so she can't clear-up all my wondering about her motivations.
The Shadow People begins with the Summer of Love in California, although no specific years are given. The narrator, Dick Aldridge, works for a "hip" newspaper in the Berkley area. His girlfriend Carol is an up-and-coming photographer. Although they are deeply in love, one night Carol storms out of Dick's apartment after an argument. She's gone for several days and Dick decides to check out her basement flat. He finds evidence of a struggle, and decides to go to the police. After the police shuffle him off, Dick takes a bus out to Monterrey to see if she's staying with an older couple they both know (perhaps a stand in for the author and her husband?). Dick finds the isolated house vacant with no sign of Carol or the older couple, but plenty of uncollected mail in the box. And on the way back he runs into a fringe character known as Carl Hood, who mentions Carol may have left "the skin of the world."
Still searching for Carol, he later encounters, Fay, the maid at his room in the Shasta Hotel. She also mentions that Carol may have "left the skin of the world." Now Dick has to know what this all means and begs Fay to tell him. She doesn't tell him much about who abducted Carol, but does show him the path to an underground world where his girl friend may have been taken. And so begins the crux of the book.
Dick, taking food with him (Fay has warned him against eating or drinking anything in the underworld), makes the perilous journey underground from an isolated cellar to vast caverns, until he crosses a subterranean river into the world of the "silent people". Along the way he picks up an enchanted sword (which appears to be a Wiccan ceremonial sword from the description) which pulses when it senses danger. And there is plenty of danger in this underworld.
The underworld is populated by elves, who a distantly related to humans. They come in several varieties- gray, black, green, and white. All are dangerous, but more to each other than to the humans on the surface. On occasion, they make foraging trips to the "bright world"(surface) and steal whatever they need. They feed primarily on atter-corn, a bitter meal made with psychoactive fungus, which produces hallucinogenic effects. But they also feed on human flesh when they can get it. Dick is attacked by them several times, but they seem to be incapable of much group action, since any blood spilled during a confrontation drives them into attacking each other.
I don't want to spoil too much of the plot, but Dick does eventually make it back to the surface. He finds three years have passed (time passage being different in the underworld), the Summer of Love squashed, and the forces of reaction in control. The novel shifts gears at this point, turning into another "winter of our discontent" book. This is what leads me to believe the first section was mostly written years before the second, with the latter written to make the narrative more "relevant" to the current target audience.
And it's the above-ground final section of the book where it runs out of gas. There's some kind of nascent fascist state in formation, but we never get much of a picture of it. People are required to wear ID tags, but you never find out how this came about in the three years Dick was underground, other than a brief mention of law-and-order politicians. There's rioting in the street and some mentions of government conspiracies. The book even mentions the CIA may want the atter-corn for chemical warfare, but this reads as an afterthought, instead of a crucial plot device.
Finally, three years have allowed robotic devices to be created which can police the population and run bulldozers. There's a few pages where Dick discovers how the hills around Berkley where removed accidentally on purpose and used to fill in the San Francisco Bay. This came about in three years? I know people believed anything was possible in the 60's (the US did put a man on the moon), but such a time scale is pushing the willing suspension of disbelief.
What really frustrated me were the characters of Carl Hood and Fay. Carl turns out to be some sinister figure with connections above and below ground. But you never really find out who or what he's working with or toward. Fay has more information about the underworld than she lets on, but her role in the novel is never fully resolved. There's defiantly a relation between both characters, but we don't find out what it is till the end of the book. And we never find out how said relationship figures into the big picture.
In conclusion, The Shadow People is a good book, but could've been a great one. We may never know why a writer of Margaret St. Clair's caliber left so many loose ends in the novel. But she did create a horrifying vision of the underworld which influenced many writers.