This is the first title in John Marsdens wonderful trilogy (now 4 books) about a group of teenagers whose land is suddenly thrown into the chaos of war.
The seven go camping in a remote and tranquil spot called Hell. When they return they find their homes destroyed, families taken prisoner, animals dead, and foreign speaking soldiers walking through their town.
The only safe place for them is back in Hell. From here their battle for survival and freedom begins fighting the enemy, surviving as friends, dealing with death. How do you survive war when the only battles you have known are between friends?