Anna Gallagher and Liam Harrison are happily married, have successful careers and when Liam's promotion comes through, they plan to start a family. That's until something happens to turn their world upside down. Anna's sister, Rachel is married to Gary, is a stay-at-home mum to Alex and is expecting her second child. Everyone is delighted with the news except Rachel. The truth is she is horrified at the thought of becoming a mum again. Jill is the girls' cousin and best friend and knows exactly what makes them both tick. Unfortunately, she can't seem to help them understand each other. The Gallagher Girls have hard times ahead but when the going gets tough, will blood really prove thicker than water?