The Earth was invaded. Not with spaceships or death rays, but with a "look". Something appeared in the sky one day, and it started changing anyone who looked at it. Those who saw it became "lookers", taken over by alien intelligences, able to spread their infection simply by meeting the gaze of any uninfected human (or "the overlooked").
Since a plot in which the entire world population is taken over probably results in a very dull story, approximately one percent of people are immune. This immunity takes several forms, depending on which part of the process of being taken over the person is immune to. These immunities might stop the process entirely, only stop the first half, turning them into Judas Goats, or only stop the second half, leaving them a useful detection tool for finding lookers. (Imagine those dogs in the Terminator films.)
And that's where Roxanne comes in. Her family have all been turned, but she remains living with them out of a sense of loyalty. This persistence is difficult, but rewarded when one day her sister wakes up from the control, and gives her a vague warning about the danger the resistance is in. This pulls her deeper into the human fight back, getting involved in the smuggling of people and information.
I've listened to the first series, and it's building a compelling plot. The resistance have to take terrible risks and awful decisions in order to survive, and struggle with internal politics. The lookers are remarkably creepy, with this weird "hmm" noise when they converse. They've got hints of the Yeerks from the Animorphs series.
It's an excellent voice cast, with the grizzled commander, spirited academic and rebellious teens. They've got sparky dialogue, and are all written pleasantly distinctively. The series is a slow burner, but always has enough going on to keep me listening. There's already a second series out and I think I'm going to have to put that fairly high in the "to listen" queue.