The Ruml were highly intelligent creatures. They had an elaborate civilisation, advanced technology and a strict moral social code - moral according to their values. They had already over-run six worlds, exterminated the native life and colonised the planets.
But an ordinary citizen of Earth, Jason Barchar, was able to penetrate the mind, think the thoughts, see the sights, feel the sensations of one of the Ruml. And on Jason depended the fate of the world - for the Ruml were preparing to invade Earth.