[1] Ellie Linton goes out camping in the bush for a week with her friends Homer Yannos, Lee Takkam, Kevin Holmes, Corrie Mackenzie, Robyn Mathers, and Fiona Maxwell.

When they return to their hometown of Wirrawee (a fictional town located somewhere in rural Victoria) they find that all the people are missing and their pets and livestock are dead or dying.

Ellie's group is spotted, and pursued by the enemy and, in order to escape, use the fuel tank of a ride-on lawnmower to create an improvised explosive.

After a protracted chase that sees several soldiers killed, Lee is successfully rescued and returned to the safety of Hell but not before they discover Chris Lang hiding out in his house after his parents were away on a business trip.

The teens decide to raid nearby farmhouses, searching for food and other supplies, and then retreat to Hell to establish a base camp for themselves.

Horn Book Magazine said that Tomorrow, When the War Began is "a riveting adventure through which Marsden explores the capacity for evil and the necessity of working together to oppose it.

[5] In 1996, the American Library Association (ALA) named Tomorrow, When the War Began as one of the best young adult titles published in America in that year.

[7] In 2000, the Swedish government selected Tomorrow, When the War Began as the book most likely to inspire a love of reading in young people, and financed the printing and distribution of the novel to teenage school students in the country.

In June 2009, Screen Australia announced that it would fund the development of the feature film to be produced based on the novel, to be written and directed by screenwriter Stuart Beattie.