Silence is Deadly (Doubleday science fiction)

Twenty agents of the Galactic Synthesis were missing on the Silent Planet of Kamm - the victims, it seemed, of the most powerful death ray the universe had ever known. But how could the primitive technology of the Kammians have produced such a weapon? And why had they unleashed its power against the Synthesis? It was Jan Darzek's mission to find out. Surgically altered to resemble the natives of Kamm, he travels to that eerie world where all life forms are deaf and the only communication ois through sign language.