Warning! Watching the intense Australian horror-thriller Killing Ground can cause an extreme physical reaction, as writer-director Damien Power discovered when the film played at the Sundance Film Festival earlier this year. “This is a great film to watch in a crowded theater and you know people are keen to see a movie if they are lining up in a blizzard at midnight,” says the filmmaker. “But I remember one session where this guy jumped out of his seat and it looked like he was dancing in pain in the aisle. [Laughs] I said to someone, ‘Is that guy alright?’ He kept watching, but he could not stay still. He just could not contain himself.”

Killing Ground stars Harriet Dyer and Ian Meadows as a couple on a camping vacation in the Australian countryside. “It’s a story about a young couple who go to an isolated spot, but when they get there they find a car and a tent but no sign of the occupants,” says Power. “They decide to stay because they’ve come a long way, and it’s a great spot, but they become increasingly uneasy when the campers fail to turn up. Then, the discovery of a child wandering in the woods is the beginning of everything going very badly.”

Very badly, in fact. Not that the experience of dreaming up and then making this brutal tale has put off Power from going camping himself.

“The funny thing is that, when I started writing the film, I didn’t have kids myself, but by the time I stepped out on set, I had kids, and we had become a family that goes camping,” says Power. “I have to say that my wife (Rachel Power) is my script editor and she edited Killing Ground. We really only go camping at very populated camp sites. We don’t camp in the middle of nowhere.”

Killing Ground will released in theaters and on demand July 21. You can exclusively watch the film’s trailer above.