A race of aliens who are non corporeal go from planet to planet looking for hosts. They come to Earth and basically take over human bodies. Now it's believed that once they take over a body all memories of the previous inhabitant are gone. And there are some humans who have remain hidden from them and are basically a resistance movement. So an alien charged with locating them known as the Seeker captures one of them a girl named Melanie and puts one of them who is known as Wanderer in her body, in hopes of finding out where the humans are. But Melanie for some reason is still there and she convinces Wanderer not to say anything to Seeker. Wanderer feels empathy for the humans. When Seeker is disappointed at her lack of progress, she informs Wanderer that she'll be removed and placed in a new host and she will be placed in Melanie. Melanie knowing she can't convince her the way she convinced Wanderer convinces Wsnderer to run away and they can meet with the humans. Eventually they find...