The film begins with a video log by Ellie Linton. She asks the camera how she can tell their story. She suggests to herself “from the beginning.”
Ellie, a high school student in the fictional rural New South Wales town of Wirrawee sets off on a camping trip to a remote valley known as “Hell’s Gate”, or simply “Hell”. She is joined by her close childhood friend Corrie McKenzie, Corrie’s boyfriend Kevin Holmes, Ellie’s next-door neighbour Homer Yannos, her high school crush Lee Takkam, and her friends Robyn Mathers and Fiona “Fi” Maxwell. During their second night camping, Ellie wakes to a sky full of military aircraft.
Returning to Wirrawee, the group finds their homes abandoned, without power, internet or telephone service. From a hilltop, the group sees that the only lights are at the hospital and the showground. Upon reaching the showground, they find that the townspeople are being detained by a foreign military force. Ellie witnesses a man being shot in the head, and in her horror retreats too quickly, being spotted by a searchlight. They flee but are pursued by soldiers into the backyard of a house. Ellie explodes the fuel tank of a ride-on lawn mower, eliminating the soldiers. In the confusion, Lee and Robyn go missing.
Hiding at Corrie’s house, the group witness an RAAF jet fighter being shot down by enemy aircraft. When an enemy helicopter performs a close examination of the house, Homer shoots out its searchlight. The group barely escape as a jet destroys the home.