12-year-old Millie and 15-year-old Lauren's parents have split up, so the sisters are constantly swapping living with 'Mum' (Sharon) and 'Dad' (Tony). Millie loves the upsides of her new family set-up; two Christmas celebrations, two birthdays, and two bedrooms. However, the downsides are trickier, as her parents start new relationships. And the new partners have children, too — and they all want to move in. Sharon's partner Mike has a son named Craig, who is a nightmare, and Tony meets Amber, who has Fran and Jake.