Three couples, friends since high school, rent a luxurious 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 women will go into the three bedrooms. The three men will each pick a room at random. It won't be awkward later, because they won't know who they've slept with - or can pretend they don't. But when the lights come back on, one of the men is dead. No one will admit to being his partner. The phones still don't work, and now the car key is missing. They're stranded. And the killer is just getting started ...