Set against a sweeping Cornish landscape, two couples discover that their toddlers were switched at birth in a hospital mix-up, and face a horrifying dilemma: do they keep the sons they have raised and loved, or reclaim their biological child?

Living a waking nightmare, Pete and Maddie are jettisoned into the world of the other couple; Miles and Lucy. At first it seems all four are agreed on a solution, but it soon becomes clear that hidden motives are at play. How far can each couple trust the real parents of their child – or even each other? As Pete and Maddie are stretched to breaking point, they realise they will stop at nothing to keep their family together.