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 parents of the other 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.