There are people living among us, who look just like normal human beings. They've been here for a long time--waiting. But they aren't exactly like us at all. Some of them can read minds, and in subtle ways take over what your are thinking, control you for a while. They can make you love. They can make you die.
One ordinary man in San Francisco, Arthur Banks, begins to find them out, and immediately his life and his family are in danger. It's a paranoid's worst nightmare. But that's just where it starts. He may well be fighting for the survival of the entire human race.