Tomorrow when the war began is about two girls Ellie and Corrie, two bored teenagers planning a camping trip to a place behind Ellie's farm property, called Hell. .
They arrange for five other teenagers to go as well, to come along with them. They camp in hell for a week, during which the local Show/commemoration day is held, and on the day before they return, on returning from a middle of the night toilet trip Ellie sees some low flying planes go by. She doesn't make anything of it until the next morning when some of the others confirm that there were planes flying fairly low and they were fairly loud. Robyn and Lee, two of the teenagers say they heard the planes and there were a lot more than the six or so fleets that Ellie saw. .
Jokingly Lee and the others, Fi, Homer, and Kevin, suggest that it's the start of world war three, and that show day/comem day would be the perfect time to attack, cause everyone would be at the show and easy to catch and all that. .
So they set off home, back to civilization, but what's waiting for them at Ellie's is not what they'd expected. Three of the four dogs are dead, with the other one on it's way to death. And all the livestock are dead or mal-nutritioned, there's no one home and the place is far too quiet for that time of year. .
Thinking that her parents have just gone out and will return shortly, they search the house for a note, but without any luck. It's then that they start to think something serious has happened. But Fi still thinks that it could be just a coincidence, so they check the other's houses, with much the same result. .
They are then faced with the biggest question they've ever had to answer, fight or not? They end up agreeing to at least finding out where the enemy are holding the townspeople hostage; they do some reconnaissance and discover that the showgrounds are the enemy headquarters and prison camp. .
They then head back to Corrie's to take stock of their situation and think of a plan to get some more supplies back to Hell.