I Am Number 4 is the first book in a series of six. It's centered around a group of nine aliens who flee their destroyed planet, and crash on Earth. They disguise themselves as teenagers (of course -- why would you be a supermodel or a sports star when you could go back to high school?), and Number 4 realizes they are still being hunted by those who destroyed their homeworld. There's some dashes of the television show Roswell there, and probably a few dozen other sci-fi teen tales.
The teen-out-of-water story of Number 4 is familiar territory for Millar and Gough, who are probably best known for their stint on Smallville, though they also had a hand in Spider-Man 2. What I find the most remarkable about is the continued success of Frey. Who says lying about your memoirs will damage your writing career and option prospects? This is America, baby!