"Tomorrow, When The War Began" is a novel by John Marsden that follows a group of Australian teenagers who go camping in the bush. When they return home, they discover that their country has been invaded by a foreign military force, and their families are missing. The story focuses on the challenges the teens face as they adapt to their new reality. They must learn to survive, make difficult decisions, and fight back against the invaders. The novel explores themes of friendship, courage, and the loss of innocence in the face of war.