This is not really the sort of book that I read, but I was really pleasantly surprised with it. The central themes has obviously been done before - aliens amongst us, a war happening under everyone's noses but it worked well and the added component of the alien kids having to be killed in order definitely added a nice element to it. The central story is about Number 4 who we meet after Number 3 is killed. Knowing he's now next on the hitlist he and his guardian, Henri flee again and land in a new town ready to settle down for the next few months until they get a sense of danger. It's in this town that Four, now known as John, starts a relationship with Sarah, a feud with her ex-boyfriend Mark and a friendship with the conspiracy theorist Sam whilst training in his newly developing powers. 
 There's a lot about the book I really enjoyed - I found the characters enjoyable and well written (my favourite was Henri and I was almost wanting a little more about his past prior to guarding Four) but I found it hard to but John as a 15 year old. Admittedly I'm sure a lifetime of fleeing for your life and being on the clock would mature you, but I am glad that they appear to have aged him in the film. I also thought that the final battle was actually maybe a little too big as weird as it sounds. I do enjoy an against the odds tail as much as anyone but the sheer scale of it was perhaps just too out there. (which for an alien book I guess is saying something. lol) 
 I'm looking forward to reading the follow up book as the author has created a really good foundation for the series and I'm going to be interested in seeing how it develops. 
 It's definitely something worth reading and even as someone who isn't a fan of the genre I found it a quick and easy read.