Sinister Barrier Author:Eric Frank Russell SIN EATERS -- a future where the human race is owned and operated by the invisible Vitons, parasites that feed on human pain and anguish. The Vitons are only visible when humans come into contact with a certain combination of chemicals. After several people use the combination of chemicals painted on the skin and die... more », the person investigating the suspicious deaths is puzzled by the victims apparently insane actions.
Investigating an epidemic of deaths among the world's leading scientists, Bill Graham learned their terrible discovery: Earth was, and had been for centuries, controlled by aliens! The alien energy beings fed on human emotions. To cultivate their 'food' they manipulated Earth affairs to create war and strife, the sources of the human fears and passions which the aliens craved.
Now their machinations were leading up to a devastating world war. They would feast finally on the self-destruction of the human race. Somehow, Graham and a hand-picked team of scientists had to stop the aliens before it was too late. But even thinking about the enemy could bring death...« less
Don't you just love early science fiction? Original copyright 1939. A lot like Flash Gordon or Doc Savage, only without as much hokiness. Scientist cum G-Man. An old book, but a fun read.