It's been a few years since aliens have taken over the bodies of virtually every human on the planet. The aliens look like brightly lit jellyfish and are inserted into the back of the hosts' necks. Earth is just the latest planet they have taken over. Melanie Stryder, her boyfriend, and her younger brother are out getting supplies when they are cornered by the aliens. They escape and she jumps through a window. She survives and is implanted with an alien named Wanderer. The one who does the procedure is The Seeker and thinks that Wanderer will lead her to the human resistance group. But Melanie's personality still remains--and talks with Wanderer, convincing her that what the aliens are doing is wrong. Melanie/Wanderer flees out to the desert where they encounter Melanie's uncle, Jeb (William Hurt). He is in charge of a group of human survivors who have a colony in the caves. They see she's clearly an alien because of her glowing eyes and don't trust her. But she falls in love with a human, which complicates things since Melanie's boyfriend is there.
This is an interesting enough alien invasion movie, a young adult version of INVASION OF THE BODY SNATCHERS. However, I foundthe internal dialogue between Melanie/Wanderer extremely irritating.