They came out of the great abyss which lay around the Earth, from the planet of a star so distant that it could not be seen with the naked eye. Their purpose was survival and the conquest of Earth. They were alien and possessed a mysterious force which lay at the very origin of human comprehension; the ability to enter into a man's mind, to make him think the thoughts they chose, to make him hear and see and feel the things they wanted.

Against such a force there seemed no defence; for who could say that the man or woman by his side was not motivated by one of these creatures? Who could say that his own thoughts and senses belonged to him and not to some ''thing'' seated in some alien way inside his brain?