Late at night, Abi and Ben are driving home down foggy country roads, arguing about having had to cut short their weekend away. Abi's driving, but her eyes leave the road for a moment as she turns to say something to Ben - just as he gasps. A man is in front of the car, waving a torch. Abi swerves to avoid him. Ben tells her they should stop and go back, but Abi refuses. It's dark, the roads are isolated and they don't know this stranger. But, as Abi turns the corner ahead of them, they see a broken-down car. Every instinct is still telling Abi to drive on, but then she notices the woman holding a car seat with a baby in it. Would you stop? For a moment, Abi hesitates, but they can't leave a mother and baby on the side of the road. Agreeing to give the family a lift, they set off again. But now these strangers are inside their car and it might be the worst mistake they have ever made.