The title stirs your curiosity, but not for long. Nine teens have survived the mass annihilation of the planet Lorien. They possess special powers - or "legacies" - and flee to earth. They are bonded by a mysterious curse, where they can only be killed in a set order. Numbers One to Three are dead.
Number Four (Alex Pettyfer) lives a nomadic life with guardian Henri (Timothy Olyphant), constantly moving to avoid the Mogadorian Army. Soon he's fed up with his lifestyle - he's actually met a girl, Sara (Dianna Agron) - and decides to take on the army, with the help of Number Six (Teresa Palmer) and Sam (Callan McAuliffe), who believes his dad was abducted by aliens.
Agron, primarily a TV actor (most notably in Glee), seems awkward in the semi-romantic scenes with love interest Number Four. In other words, she looks like she's acting. Pettyfer is not much better - he comes off more as a model, less a superhero.
Along with the dull, stiff dialogue, and lack of chemistry between actors, the film is essentially a mess.
Leave the superhero stuff to the experts at Marvel.