After ending up in bed together following a school reunion, childhood sweethearts Matthew and Katy agree that they must never see each other again. So all is forgotten - until, eight months later, a shocking meeting at an antenatal class... After years of desperately trying to conceive, Matthew and his wife Alison are expecting twins. As if that wasn't enough, Katy admits that he may or may not be the father of her soon-to-arrive baby. Love and life are about to get messy for Matthew and Katy - not to mention their other halves...