As we're all aware, sometimes when a book gets a film adaptation, the story is torn to pieces. Just look at Phillip Pullman's beautiful His Dark Materials series. New Line released The Golden Compass in 2007, which is apparently one of their most expensive movies to date. Visually, it was a masterpiece (I mean, it's really worth watching the movie just for the incredible VFX, particularly the ice bears), but it softened a lot of the atheist themes of the book (though not enough to prevent harsh criticism about it being violently anti-Catholic) and rearranged many of the events in the book for absolutely no reason. This, and the fact that the whole thing was badly paced, caused the movie to flop; a brilliant book flopped, even after New Line emptied their wallets throwing money at the production.
Similarly, the first Percy Jackson movie was almost indistinguishable from the book. While I understand that the Percy Jackson books are oddly structured (that's not a criticism, as I'm a big fan of the series and enjoy its picaresque style) and would not easily leap to the screen, I think that Fox handled the material really badly, probably worse than New Line did with Northern Lights. They shuffled everything around to fit the Hollywood formula, skipping over loads of important plot elements, characters, and the series' underlying villain completely. However, it was still reasonably enjoyable.
So, I Am Number Four: The Book. First book in the Lorien Legacies series. Written by James Frey and Jobie Hughes under the pen name Pittacus Lore. Young adult sci-fi romp.
And then, I Am Number Four: The Movie. First and now probably only movie in a planned but shelved series. Directed by D.J. Caruso and, though you wouldn't guess from watching it, produced by Michael Bay, all for Touchstone Pictures. Teen sci-fi action movie (sort of).
What's it all about? Well, there's this guy, called John Smith. He's fourteen (but played by 23-year-old Alex Pettyfer), and he's one of only eighteen remaining aliens from the planet Lorien, which was invaded several years before the story starts by the villains, the Mogadorians, an evil race who use life force to sustain their technology. The nine Lorien children sent to Earth are protected by a special charm that means that they can only be killed in sequence. However, that doesn't help John; the first three are dead, and he is Number Four.
That's the basics of the premise. There are lots of details about Lorien's core and about Lorien's alien magic, and lots of backstory about life on Lorien and John's memories, and all these flashbacks of the war and explanations about why some Lorien-people have powers and some, like John's protector Henri, don't, but none of that's important. Or at least, Touchstone Pictures didn't think so. Everything I've just mentioned is left out of the movie, and that's not even a quarter of the total omissions.
So what's in the movie, then? Well, the bare bones of the story: John moves to a new town in Ohio, knowing that he's next. He makes a friend in Sam Goode, an alien conspiracy theorist, and a girlfriend in Sarah Hart (still a better love story than Twilight), and then there's this jerk called Mark James...it's all very simple, really, and aside from a few props here and there and the alien bad guys themselves, there's nothing very sci-fi about it at all. John could just as easily be a young undercover spy (perhaps in the vein of Alex Rider?), on the run from some enemy agents. The sci-fi almost feels unnecessary...until the end.
There's the school battle, and in the movie it's awesome. It's a little different to the book, but it's still cool. And Number Six is introduced.
This is where the comparison gets interesting, because Six is actually a better character in the movie than in the book. I'm serious - though Six has just as many lines in both, Teresa Palmer shows us some emotion in the movie, whereas in the book Six doesn't really do much except fight. Her entrance is an unexpected twist, but a bit flat. It feels like a tag-on. In the movie, Six is introduced about an hour earlier through some little bits that are hinted at in the book but never explicitly described, and they work a treat. They make her a serious badass.
The villains are much better as well, even if the film does make them seem slightly silly. While the gangster-styled Mogadorians of the book are imposing, the gill-nosed, supermarket-frequenting Mogadorians of the movie are both funny in their semi-assimilation of human technology and culture, and also hugely menacing; the way they dispose of their loose ends is beautifully sadistic, especially in tandem with their humorous side. My only comparison is the ear-cutting scene in Reservoir Dogs (which was undoubtedly a huge influence on this). Again, watch the movie for yourself to see what I'm talking about. I don't want to write spoilers, and I don't think I can do the scene justice anyway.
However, the lack of any Lorien whatsoever does make me a bit sad. Though the book isn't amazingly written (not bad, just not anything overly special), the concepts described about Lorien and why some of its inhabitants have powers is kind of beautiful. I won't put it here; it's not a major spoiler or anything, but you should read it for yourself. It's more powerful that way. There are also lots of flashbacks to John's family on Lorien and the life he had there, and they flesh him and a few other characters out massively, as well as providing some depth to a later plot development (involving a gecko and John's grandfather). I know the movie had a limited budget, but it would've been nice if they'd have made a bit of an effort. The book has such heart and depth, whereas the movie focuses on the teen love-story aspect a little more than is necessary and makes the science just out-and-out sci-fi. No magic involved.
All in all, I'd say watch the movie and then read the book. I enjoyed the movie, but if you come from it having read the book and expecting the same warmth, you'll be disappointed.
P.S. the book has lots of swearing in it, which is just one of the things that makes it 'young adult' rather than 'teen'. The movie didn't, and was firmly 'young teen'. Complete change in maturity level. Know your audience. Just sayin'.