(This post originally ran in slightly different form on November 6, 2005.)
This is the other half of that Ace SF Double I wrote about last week, and like Milton Lesser's RECRUIT FOR ANDROMEDA, this early novel by Robert Silverberg, writing as Calvin M. Knox, is pretty good. It's also a good example of taking a standard plot from one genre and transplanting it to another. In hardboiled mysteries, you've sometimes got the lone government agent out to smash the dope racket in a corrupt town. In THE PLOT AGAINST EARTH, you've got the lone Terran agent out to smash the hypnojewel racket in a corrupt galaxy. Silverberg makes it work just fine and his prose is always a pleasure to read.
I don't know if this story was first published in one of the SF digest magazines, but it certainly seems possible, especially given the fact that the book is dedicated to Robert A.W. Lowndes, one of the magazine editors who bought a lot of Silverberg's early fiction. I like the cover on the Ace edition, which is by Valigursky, because not only is it striking but it also depicts an actual scene from the book.