Pete answers the door to a parent’s worst nightmare. On his doorstep is a stranger, Miles Lambert, who breaks the news that Pete’s two-year-old, Theo, isn’t his biological child after all – he is Miles’s, switched with the Lamberts’ baby at birth by an understaffed hospital. Reeling from shock, Peter and his partner agree that, rather than swap the children back, it’s better to stay as they are but to involve the other family in their children’s lives. But a plan to sue the hospital triggers an official investigation that unearths some questions about just what happened on the day the babies were switched. And when Theo is thrown out of nursery for hitting other children, Maddie and Pete have to ask themselves: how far do they want this arrangement to go? What are the secrets hidden behind the Lamberts’ smart front door? And how much can they trust the real parents of their child – or even each other?