"Tomorrow, When the War Began" is a young adult novel by John Marsden that follows a group of teenagers who go camping in the Australian bush. When they return home, they discover that their country has been invaded and their families taken captive. The story explores their struggle for survival and the challenges they face as they adapt to a new reality. The main character, Ellie Linton, along with her friends, must learn to fight back against the invaders while grappling with the moral dilemmas of war. The novel highlights themes of friendship, courage, and the loss of innocence in the face of conflict.