Three couples, friends since the university athletics team, travel to a house in the mountains for an unplugged weekend of drinking and bushwalking. No internet, no phones, no stress. On the first night, the topic of partner-swapping comes up. It's a joke - at first.
Not everyone is keen, but an agreement is made. The lights will be turned out. The three men will go into the three bedrooms. The three women will each pick a bedroom at random. It won't be awkward later, because no one will know for sure who they've slept with - though each guest is privately sure that they alone will be able to tell.
But when the lights come back on, someone is missing. A search of the house and the surrounding bushland turns up a body.
Five people remain. They have no way of contacting the police. Nor can they leave - the key to the car is missing. And the killer is just getting started.
