I Am Number Four has so far done a bang-up job of failing to make itself known to the general public to the point where a straw poll conducted exclusively for The Incredible Suit revealed that out of two conveniently-passing people, neither had heard of it. Extrapolate those figures and it soon becomes clear that the entire population of the universe is blissfully unaware of the film's very existence.
For the benefit of everyone then, here's the plot in a nutshell:
Why they're trying to kill each other is unclear. What is clear, thanks to some hackneyed character signposting, is which are the good aliens (conventionally good-looking humanoids) and which are the bad aliens (conventionally hideous humanoids with long black coats, tattooed heads, red eyes and pointy teeth. Think bald Gary Busey).
Cuboid-headed charisma vacuum Alex Pettyfer plays Number Four, the good alien, who uses his alien powers to suck all of the film's fun into a black hole where his personality should be. Pettyfer's remarkable talent and range can be demonstrated by this tired old visual gag:
You may remember Pettyfer from Alex Rider: Stormbreaker, a teen-targeted potential franchise which stalled after just one film. Only time will tell if his presence here causes the same fate to befall this teen-targeted potential franchise (Crazy prediction: It will).
As Number Four is the most hunted alien in the galaxy he does his best to stay hidden by going to school in broad daylight every day, rather than staying at home and playing with all the product placement provided by Apple. At school he meets a series of stereotypes, one of whom (clue: not the jock or the nerd) he falls in love with despite the fact that she's a) the world's least convincing photographer and b) intent on using up the world's supply of question marks in her text messages.
Eventually there's some fighting and shooting and an unintentionally hilarious CGI dog which probably shouldn't remind you of The Mask, but none of it approaches anything that could be described as original or interesting.
I could go on and on but that's the film's job. Basically if you enjoy films in which Timothy Olyphant is the best thing, then not only is I Am Number Four for you but you also need to watch a lot more films.