Robert Silverberg 
Plot Against Earth [EPUB ebook] 

NEVER FOLLOW A FALLING STAR!The humanoid worlds of the galaxy were alarmed! Somehow, somewhere the mind-destroying hypnojewels were being trafficked in. An uneasy Earth, newcomer to the ranks of the civilized planets, sent Lloyd Catton to the Interworld Crime Commission on Morilar to investigate. Although the Commission had made little progress until then, after his arrival things started to happen fast.For it didn’t take Catton long to realize that the hypnojewels were but the thin edge of a murderous wedge that was calculated to shove the Earth back again into the helpless isolation of a world returned to savagery.