From the back cover:
The world was coming to an end...but only the toti-potents knew it. They were the instruments of the alien invaders.
Once they had been ordinary men. But when the invaders from space took possession of their bodies, they became immortal and perpetually young; able to read minds and predict and change the future; possessors of weapons infinitely more powerful than any Earth had ever known. And they began to hate men.
But because, outwardly, they still looked and acted like everybody else, there was no way to tell who they were--until they attacked!