Catherine Saint John-Burke is an independent, sophisticated British woman living in London's Chelsea. Her world is turned upside down one day when she comes home to find an uncouth Kiwi woman, Shirley Zachary, drinking beer on her sofa. Shirley announces she is Catherine's long lost half-sister. As far as Catherine is concerned, the only thing Shirley has lost is her mind.

Undaunted by Catherine's doubts, Shirley claims that her father, whom Catherine thought had died before she was born, is still alive and trying to make claims on both their properties following the simultaneous deaths of both their mothers. Both girls eventually agree to work together to track down their con-man father in order to get rightful ownership of their inheritance. Along their journey they discover many things, but most importantly, they discover the meaning of "sisterhood".