Seven teens from a (fake) rural community in Australia go camping, and while they're away from civilization an army invades Australia, starting with their town because of its strategic location. When they do get back to civilization, it is to find their homes abandoned, their pets dying or dead, and the streets of the city are teeming with rather trigger-happy soldiers. Drama, explosions, soul-searching and character growth ensues.
This was a very enjoyable book not only for the action-packed scenes (which are bound to be very entertaining in the movie), but also because of the growth and shift in group dynamics the characters go through. It wasn't a character-driven story at all, though (come on, there's a war going on! This is great action-story time!), which was a welcome change from the other stuff I've been reading lately.
I'm not sure if I want to read the rest of the series, though; after such a good start, I'm afraid it will all go a bit downhill. But still, maybe John Marsden has written a good follow-up to this novel? In any case, I recommend this novel; it's not too long, it's not too short, it's entertaining and I liked it.