Pete Riley answers the door one morning and lets in a parent's worst nightmare. On his doorstep is Miles Lambert, a stranger who breaks the devastating news that Pete's son, Theo, isn't actually his son he is the Lamberts', switched at birth by an understaffed hospital while their real son was sent home with Miles and his wife, Lucy. For Pete, his partner Maddie, and the little boy they've been raising for the past two years, life will never be the same again.