Robert Silverberg

Those Who Watch is a science fiction novel by Robert Silverberg, first published by Signet in 1967. The novel concerns a trio of alien explorers, each one surgically altered so that they outwardly appear human, who find themselves separated, and permanently stranded on Earth, after their ship explodes while hovering …

Thorns is a science fiction novel by American author Robert Silverberg, published as a paperback original in 1967, and a Nebula and Hugo Awards nominee.